I remember many many years ago before i decided it was just guys for me, a girl and male friend and myself had some fun with this, and other experiments, we guys were both similar size, i had a little more girth. i prefered going underneath and feeling him thrusting along side me, the girl enjoyed it and i think she'd encouraged it as for her pleasure and as we didn't stick to purely straight activities she really got off on us guys being 'close'. Reading this thread i'm suprised we didn't fail dismally as it was a spurr of moment thing,no working up to it-other than all very aroused having had a few days of cheekiness. I think mentally if girl wants it she will know what she's doing to get what she wants. If guy forces it on her then nothings going nowhere!!