The Posterior Fornix can be stimulated during doggy style. (Anterior Fornix in missionary.) They are similar to the g-spot, with some people preferring fornix orgasm to g-spot or clitoral stimulation. You aim above the cervix with the tip of your dick or fingers and stretch that area.

This depends on the anatomy of both partners. It’s also a skill that needs to be trained. However, if you can make it work, and the recipient is sensitive to it: fireworks! Like, grunting, moaning, and prayers from a bad porno level of good.