No vegetation features spawning on the last two sections of jigsaw structure

I have a jigsaw structure which spawns as multiple vertical segments, in the screenshot ive seperated the jigsaw pieces. The vegetation is spawning on all sections except the last two.
I suspect that this is because the structure is at the end of it's "depth" and so can't place any more features which is how it places vegetation, and the final piece is the fallback so that gets placed after the "depth" has essentially run out (if that's how it actually works). Is there any way to fix this while keeping the structure the same height? I want it as high as possible, it's currently limited by what I think is the maximum size for jigsaws.