Benny (and every other partner I've had) has woman-on-top sex in the "normal" way--man holds more or less still, woman moves back and forth or up and down. If the man wants more control, he grabs the woman's waist and guides/shoves her movements.
Alan does it differently. He wants me to get on top, leave an inch of space, and hold still while he thrusts up from the bed. It looks terribly strenuous to me, but he seems to love it and if I start moving he'll tell me to stop. Just let him do his thing.
It feels fine to me, but I always think it's funny that he doesn't know he's weird. There's no awareness that "It's weird but it works for me;" as far as he's concerned, that's just how you do it. The first couple times he was amused that I didn't instantly understand what he was trying to do.
Sex is such a private thing that if you're straight and don't watch or read hardcore porn you never really know how your gender "normally" participates in sex. I'm sure he got hints from other girlfriends and whatnot, but in a sense, Alan invented sex himself.
It's amazing he got as many things right as he did. Coulda ended up in my bellybutton or something.