Facing up and with legs wide open she lets him in by the front. It's a world of difference as far as sensations go, for the clitoris and labia achieve full contact with his pelvis and crotch rendering penetration easier by circular movements. She is able to contemplate his buttocks that are up for grabs.
He can play with her feet, play with her and his genitals manually for further stimulation as she probes his ass.