From my own personal experience, it's really all about the bump and grind. The actual penetration doesn't do much. It's the act of bumping and grinding your bodies together that does the trick. That's where the woman gets her clitoral stimulation.
With my ex, if I finished before she did, I could stay in the position I was in while she grinds her pelvis against mine, and she could finish off that way. So it's like what Vashti said... It's either her own (or your) fingers touching the clitoris, or your body touching it.
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