"A kitsune can assume the appearance of a specific single human form of the same sex."
But I don't see anywhere that they are limited to their kitsune size. So I would think that a 5'6" 150 lb. kitsune could assume the appearance of a 6'0" 180 lb. human.
Yes. As long as you remain a medium creature, and within what a human could actually be, your single human form isn't limited to your kitsune's height and weight.
