Yes, indeed. I think it's better suited for loose rocks, or on tree trunks or so.
Anyway, got it working with the centers dying out again, and three species non overlapping. I do think the patch size should be increased. It's a very diverse size now, but can also be pretty all-the-same.
The big one (7) has some nasty cracks, which I took out in the smaller test. Done with this again.