I had a partner years ago that responded wildly to deep penetration. I could reach her cervix from most positions, and she seemed to enjoy cervical nudging. The wildest though was when we would start out doggy style and then flatten down to the bed - I would straddle her and work up to deep thrusting. When I would push all the way in, I could feel a little resistance just past her cervix and all I had to do was push in and keep some pressure on that spot, and she would have the wildest spastic orgasms I've ever seen. I was a little worried at first because I was afraid she was having a seizure, but soon learned that all was well. We ended up in this position nearly every time we had sex. Because of the shape of my penis, I'm sure it was the posterior fornix I was pressing on.
Unfortunately, in my experience not all women respond in this way. With my first partner ever, I couldn't press at all doggy style because it caused her pain.