Make sure you keep a super arched back for optimal ham/glute stim. I like either feet wide enough to just slide my stomach between my knees at the bottom or feet just under the hips, heels about 6" apart.
The close stance version hits your glutes harder than a drunk closet-gay at an evangelical youth camp. Other wise its all hamstrings.
Pair it with bulgarian split squats for the ultimate lower body assistance work.