Minecraft: 1.10.2
Mod Version: Botania r1.9-339

I'm running on a very slightly modified version of AllTheMods Lite (Mekanism removed, Agricraft removed, Iron Backpacks and Elevator Mod added).

According to the Lexica Botania, the Rod of Terra Firma does not work below Sea Level. However, it doesn't seem to be working at sea level either. I can only get it to work when my minimap shows Y Level 64, but sea level is Y Level 63, one below. Since I built my base on level 63, it means if I want to flatten terrain I have to do it one level higher, and then remove a complete layer of dirt (obviously, really annoying).

Here I am standing at sea level, holding right-click on the rod, and nothing is happening. The rest of the dirt seen is me standing at level 64, one above.

Is this an off-by-one error, or is sea level different in AllTheMods or something?

According to the Minecraft Wiki, sea level (altitude of the top layer of water blocks) was y = 63... until Beta 1.8, where it was changed to y = 62.

y = 63 has been dry land ever since.

Line 114

This is where it checks for it, all it does is check if you are below the sea level as provided by MC.

however its probably Line 112 that's causing it as its offsetting the position it checks against down by 1 block.

world.getSeaLevel is 63 by default, by the way

afaik sea level in minecraft has always been at Y 64

its probably the downwards offset that's causing it then.