I don't have Apollo Maximus, so can't speak directly of that figure, but in general when doing an arms above the head pose, you will get better results if you implement approximately half the rotation in the upper arm and the other half in the collar.

Poser figures in general do not handle arms above the head poses well, and you may need to do some touch-up in postwork. Another option is to try and make corrections in Poser using magnets, though this can be quite difficult.