The doctor on this website stated that some women will achieve orgasm during penetration, some will during masturbation, some wont get one at all.
if you can ride him and instead of consentrating on the up and down movement, but try to move in a sweeping movement. this should allow your clit to rub against his pelvic bone. it feels just like masturbating. this is a easy way to have an orgasm.
i usually dont orgasm only unless someone performs oral or i masturbate. but with my ex every time we had sex in the riding position i was guaranteed an orgasm.
it takes practice but it's worth a it.