By default, I can't put a blitter object on top of an iff animation, because AMOS automatically updates the surface underneath to a previous state when the blitter object is moved.
That's why so far I could only move sprites over it, because it didn't spoil it, but in that way I could move one "large" sprite over it.
In the new upload, however, there are several large blitter objects above it. It's slow, but worth a try.