If she wants you to go back and forth between her thighs until you cum, you prefer her to be:

- back to you, you grab her by the hips (she sees your sperm spurt out under her pussy and run down the front of her thighs)

- facing you, you grab her by her plump ass (she doesn't see your sperm, she feels it on the bottom of her ass and running down the back of her thighs)