use the keywords to change the pose:
Pony: 'facing towards viewer' usually means they'll be bending forwards a bit

pony: 'facing away from viewer' will give you an ass shot

pony+ illustrious: 'lying on back' with 'legs up' will have them lying on a bed or something.

Illustrious: 'from behind' for ass-focused picture
illustrious: 'facing viewer' for normal shot.