Expected behavior: Nether portals should spawn as they would in vanilla Minecraft.

Actual behavior: Building a portal above a certain y-axis level in the overworld causes the resulting exit portal in the nether to spawn above bedrock in BP 0.2.3.

Here is a screenshot of a portal I made in a shattered savanna biome with BetterPortals

Portal exit coordinates is 6, 128, -77

Here is a clip of me building a portal on the same seed, in the same location in vanilla 1.12.2.
https://files.catbox.moe/zzqxer.webm
Portal exit coordinates is 7, 83, 11

For the sake of reproducibility, the seed used is: 2525617506084080286 and the overworld coordinates I built the portal on is 50, 147, -114. Though it should be easily reproducible on any seed simply by building a portal in a sufficiently high location