Depends on how much her butt 'protrudes' and how deep in her vagina sits. If you have to go through a few inches of ass just to penetrate, that's going to be a disadvantage to a smaller guy. You can compensate by spreading her ass cheeks though.... had to do that myself for my ex-fiancee and her 45" inch hips and ass( not fat, just wide hips and an ass that stuck out a mile).