Apologies for the kind of vague use of "Offset", but I couldn't think of a better word.

Anyways! So, I've set up two celestial gateways such that one is within the overworld, and the second is within the mod The Lost Cities dimension. No matter the gateway you travel from, the resultant is that you appear to be about 88-89 blocks off of the intended target. ~17 blocks in the z direction, and ~87 blocks in the x direction. As far as I can tell, the y direction is not affected, since I would seem to spawn in the skies from either location.

Forge: 2565, at least that's what my server admin remembered off the top of his head.
AS:1.12.2-1.8.4

That...sounds like its working as intended, then. What am I missing?

Correction! I decided to use my aevitas wand so I could float on the other side of the gateway, and it would seem that the height I spawn at would be the same y as the portal in the other dimension.

Huh. I just realized something extremely important. The coordinates that I am being sent to are the exact same ones as the inital celestial gateway. Overworld portal is at x:75, y:80, z:499, and the end point (in TLC) is the same coords.

As far as I am aware, there is not a coordinate shift like the Overworld/Nether.

As for the full modpack list, what I am going to post below should be all of them, since I used command prompt to get a list of the mods folder.

1.12.1-CustomOreGen.jar
1.12.2
AbyssalCraft Integration-1.12.2-1.6.2.jar
AbyssalCraft-1.12.2-1.9.4.3.jar
AdvancedRocketry-1.12.2-1.2.6-7.jar
AoV-1.12-0.8.2.jar
AppleCore-mc1.12.2-3.1.0.jar
AppleSkin-mc1.12-1.0.9.jar
appliedenergistics2-rv5-stable-3.jar
Aroma1997Core-1.12.2-2.0.0.0.b129.jar
AromaBackup-1.12.2-2.1.1.3.b88.jar
astralsorcery-1.12.2-1.8.4.jar
AutoRegLib-1.3-15.jar
base-1.12-3.4.2.jar
Baubles-1.12-1.5.1.jar
bdlib-1.14.3.10-mc1.12.2.jar
BetterFps-1.4.8.jar
BiblioCraft[v2.4.3][MC1.12.0].jar
BiomesOPlenty-1.12.2-7.0.1.2310-universal.jar
blockcraftery-0.1.3.jar
Bookshelf-1.12.2-2.3.510.jar
Botania r1.10-352.jar
Ceramics-1.12-1.3.3b.jar
Chameleon-1.12-4.1.3.jar
ChatFlow-1.4-7.jar
Chisel-MC1.12-0.1.0.23.jar
chiselsandbits-14.11.jar
CoFHCore-1.12.2-4.3.7.25-universal.jar
CoFHWorld-1.12.2-1.0.2.10-universal.jar
CommonCapabilities-1.12-1.4.0.jar
compatlayer-1.11.2-0.2.9.jar
ContentTweaker-1.12-4.2.0.jar
Controlling-3.0.5.jar
CookingForBlockheads_1.12.1-6.3.17.jar
CosmeticArmorReworked-1.12.2-v1.jar
CraftingTweaks_1.12.1-8.1.6.jar
CraftTweaker2-1.12-4.0.10.jar
Cravings-1.12.2-1.0.3.jar
CTM-MC1.12-0.2.3.9.jar
CustomMainMenu-MC1.12.2-2.0.8.jar
CyclopsCore-1.12.2-0.10.24.jar
deepresonance-1.12-1.4.9.jar
DungeonTactics-1.12.1-0.13.9.jar
easypickings-1.2.0.jar
ElecCore-1.12.2-1.8.433.jar
elulib-0.1.11.jar
Enchiridion-1.12.2-3.3.3.jar
endertanks-1.12.0-1.6.3.jar
EnderZoo-1.12.1-1.4.0.49.jar
EngineersWorkshopReborn-1.12.2-1.0.3.24.jar
EvilCraft-1.12.2-0.10.42.jar
extraalchemy-0.3.6-release.jar
extrautils2-1.12-1.6.8.jar
files.txt
foamfix-0.8.1-1.12-anarchy.jar
forestry_1.12.2-5.7.0.214.jar
ForgeEndertech-1.12.1-4.3.0.0-build.0056.jar
Forgelin-1.6.0.jar
gendustry-1.6.5.6-mc1.12.2.jar
GiacomosFishingNet-1.12.2-1.6.1.jar
GraveStone-1.12-Graves-1.0.12.jar
GraveStone-1.12.2-Extended-1.2.6.jar
Guide-API-1.12-2.1.4-57.jar
ImmersiveEngineering-0.12-75-core.jar
ImmersiveEngineering-0.12-75.jar
immersivepetroleum-1.12.2-1.1.5.jar
industrialforegoing-1.12.2-1.6.2-106.jar
IntegratedDynamics-1.12.2-0.9.8.jar
IntegratedTunnels-1.12.2-1.3.6.jar
IntegrationForegoing-1.12-1.4.jar
InventoryTweaks-1.63.jar
ironchest-1.12.2-7.0.34.820.jar
IvToolkit-1.3.3-1.12.jar
jeibees-0.9.0.5-mc1.12.2.jar
jei_1.12.2-4.8.5.136.jar
journeymap-1.12.2-5.5.2.jar
librarianlib-1.12-4.3.jar
LibVulpes-1.12.2-0.2.7-19-universal.jar
LootTweaker-1.12-0.0.6.5.jar
lostcities-1.12-1.0.2.jar
lostsouls-1.12-1.0.0.jar
LunatriusCore-1.12.2-1.2.0.42-universal.jar
MagicBees-1.12-3.1.7.jar
Mantle-1.12-1.3.1.21.jar
mcjtylib-1.12-2.5.0.jar
MCMultiPart-2.3.3.jar
Mekanism-1.12.2-9.4.2.327.jar
MekanismGenerators-1.12.2-9.4.2.327.jar
MekanismTools-1.12.2-9.4.2.327.jar
minecolonies-universal-1.12.2-0.8.5950.jar
MistWorld_1.12.1_alpha_b_02.jar
modtweaker-4.0.5a.jar
morebees-1.12.2-1.4.4.jar
moreoverlays-1.13-mc1.12.1.jar
Morpheus-1.12-3.3.2.jar
MTLib-3.0.1.jar
multistorage-1.12.0-1.4.7.jar
NashornLib-1.9.4-1.8.77-1.3.1.8.jar
natura-1.12-4.3.0.23.jar
NaturesCompass-1.12.2-1.5.0.jar
nemesissystem-1.12.1-2.jar
NetherEx-1.12-2.1.14.15.jar
NetherPortalFix_1.12.1-5.3.13.jar
NoFov-MC1.12-1.0.1.jar
Pam's HarvestCraft 1.12.2a.jar
PersistentBits-1.12-1.0.6a.jar
plustic-6.3.2.1.jar
PrimalCore-1.12.2-0.6.9.jar
primitivemobs-1.1.3beta.jar
Quark-r1.4-120.jar
QuickLeafDecay-MC1.12.1-1.2.4.jar
RandomThings-MC1.12.2-4.0.8.jar
RebornCore-1.12.2-3.5.2.171-universal.jar
RecurrentComplex-1.4.6.jar
RedstoneFlux-1.12-2.0.1.2-universal.jar
RefinedRelocation_1.12.1-4.1.12.jar
Reliquary-1.12.2-1.3.4.724.jar
ResourceLoader-MC1.12.1-1.5.3.jar
rftools-1.12-7.15.jar
rftoolsctrl-1.12-1.7.0.jar
rockhounding_core-1.12.2-3.02.jar
rockhounding_oretiers-1.12.2-3.01.jar
rockhounding_rocks-1.12.2-3.03.jar
RoguelikeDungeons-1.12.2-1.8.0.jar
Scannable-MC1.12-1.6.2.13.jar
secretroomsmod-1.12.2-5.1.9.jar
shetiphiancore-1.12.0-3.5.5.jar
Signals-1.12.2-1.2.0-3-universal.jar
solcarrot-1.12.1-1.2.0.jar
SpartanShields-1.12-1.3a.jar
Stackie-1.12.2-1.6.0.48-universal.jar
StorageDrawers-1.12.1-5.3.3.jar
TamModized-1.12.1-0.15.3.jar
TConstruct-1.12-2.8.0.45.jar
tellme-1.12.2-0.5.6.jar
terraqueous-1.12.0-1.4.5.jar
Tesla-1.12.2-1.0.63.jar
tesla-core-lib-1.12-1.0.11.jar
theoneprobe-1.12-1.4.19.jar
ThermalDynamics-1.12.2-2.3.7.14-universal.jar
ThermalExpansion-1.12.2-5.3.7.31-universal.jar
ThermalFoundation-1.12.2-2.3.7.18-universal.jar
TinkersComplement-1.12.1-0.2.2b.jar
tinkersdefense-1.4.2.3a.jar
TipTheScales-1.12.2-1.0.0.jar
topaddons-1.12.2-1.2.1.jar
torotraits-1.12-1.jar
TrashSlot_1.12.1-8.4.6.jar
twilightforest-1.12.2-3.5.263-universal.jar
VTweaks-1.12.2-1.4.12b.jar
Waystones_1.12.1-4.0.17.jar

Within the 1.12.2 folder is
CodeChickenLib-1.12-3.1.3.313-universal.jar

Oh, is it not meant to land you at the other celestial gateway? I assumed it was to land you on top of the other one. I do apologize if this is working as intended, it just seemed very odd to me.

Ah, I see what you mean now. No it should be placing you at the other platform. I've not played with TLC, does it have any coordinate shift like the Overworld/Nether does?

Also, full modpack list with versions, please, in case it's an odd interaction.

Figured since it's been a week, I might as well ask if there's been any leeway into this issue being solved. I spent a bit of time looking through the various files I could find pertaining to the gateways, but really didn't find much about cross dimensional travel that pertained to the players coords.

I have no clue. Give me a few days to go through AS and I'll let y'all know.

@greenking13 is this still present in the AS 1.8.10 version?

After testing cross dimensionally, this bug no longer exists. It can now be closed. Also, I like the new "snapshot" the portals give of the location travelling to.