I'm assuming you mean her on her stomach and you entering from behind.
Strangely, I've seen this position listed in various resources as both a good position for long-dicked guys because it doesn't allow for deep penetration AND a good position for short-dicked guys because it allows for especially deep penetration.
I think it depends on the specifics. If she's truly flat on her stomach, has her legs somewhat closed, and has any ass at all, it should lessen the depth of penetration since your dick has to reach that much farther before it gets to the vagina. If she's got a pillow under her pelvis, her legs apart, and not much of a butt, I'd imagine it's not a whole lot different than doggy, which of course can provide a deeper penetration.
I'm a big fan of jockey specifically because it shallows the penetration and is thus the one position in which I can just hammer away with reckless abandon without fear of the dreaded cervix bump.