For women who feel that her lover’s penis size is trumping her pleasure, in cases where he is larger, you need to first be able to communicate with him on him going too deep. He’s likely getting caught up in his response, but needs to respect that there’s only so far he can go. In having him go deeper comfortably, you may just need more foreplay. (Most women need 20 minutes of foreplay for their vaginal canals to elongate enough for comfortable penetration. Otherwise, a male’s penis can knock against her cervix, causing pain.) In cases where he feels “small,” you can seek to exercise your pelvic floor muscles so that you better trip him during intercourse.
Finally, more than anything, seek to be relaxed and well lubricated, as both will help to make the action smoother and more pleasurable.