Biomes are always generated on the side of the islands, like patches. I've tried with multiple worlds, and all the same issue. It's nearly impossible to find a full-blown Poise Forest. The issue might not be on your end, I also have Better End, The Outer End, Enlightend, and Unusual End. (I reckon it is compatible with the first two.) But still, the Poise Forest is the only one to generate like this. I'm on forge 1.20.1

And also, it's a great mod! Thanks for your efforts.

This is somewhat expected when you have many end biome mods. Poise Forests can only safely generate on outer end island positions unoccupied by modded biomes.
There isn't really anything we can do about it, but you can try configuring biome weights to make Poise Forests more common or to make other biomes rarer.