This is a practice I haven’t engaged in, purely because I usually find the girth of a cock satisfying. Don’t get me wrong I like to feel Alex’s fingers waggling around inside my pussy too, he is excellent at targeting my g-spot and making me squirt.
I think my comfort range quiet literally stretches to 3 of his fingers inside me, so why would I want him to push his fist inside me. On the other hand ( no pun intended lol) if you have petite hands then you would most probably manage to get inside me up to your wrist.
Food for thought and maybe some covert observations may need to be made. In the meantime you can study this image and wonder at her flexibility. 😉