I’m fairly certain it’s a spath but LFS thought it was a Humilis?
The one to the right of what I think is the spath is an actual Humilis I’ve had a while and looks growth and shape looks very different.
I'm trying to find the article, but I believe A. spathulata and A. prostrata are now recognized as millepora. The one on the left is spath (as we know it), humilis has flattened, rounded axial corallites that are domed shaped, whereas spaths will have sharper, distinct axial corallites, sometimes flat, but not rounded. Plus the difference in radial corallites as well. Spaths are flared and flattened with pretty much one size, while humilis can be flared, but not flattened, more tube-like and difference sizes.