During rear entry (AKA doggy-style) intercourse, the head of your husband's penis is stroking the front vaginal wall. Any position that has strong front wall stimulation would do the same thing. The nerve systems in this area are the pelvic and hypogastric. The belly button side of the vaginal wall is where one concentrates motion to stimulate the G-spot, but please note the G-spot is not in the vaginal wall it is above it and as such often requires much firmer pressure and stimulation. Also it has been noted that women who have delivered vaginally have a better chance of experiencing strong G-spot stimulation, as their vaginal barrel is more flexible from having delivered. Note I did not say looser. The PC muscle at the entry into the vagina is the determining factor for tightness and can be toned using Kegel exercises.

In comparing the orgasmic sensations of a clitoral vs. a G-spot/front vaginal wall orgasm, women have said the clitoral feels more like a pulling up and in, while stimulation of the G-spot/front vaginal wall feels like a broader more all over pushing down and out sensation. I hope this answers your question. For a more in depth discussion, I cover this topic extensively in The BIG O .