He props himself up while she rests her legs on his shoulders in a sexual charged position. To do so renderig sex- pace control easier. The penetrative angle of sex is bound to remain deep largely due to her leg angle.
Holding his legs she reaches him better imposing her rhythm. The clitorial stimulation enhances along as her leg-opening squeezes him tightly inside. A woman who fancies showing off her womanly skills of sex, can play with herself for their delight.