It could be to big but when my female does that she often times grabs the butt or the side of the rat and is too lazy to find the head. Do you feed f/t? If so grabbing the rat on the scruff of the neck with your tongs and feed your snake that way so it is easier for them to get to the head.
Oh, that's actually a good idea. I just assumed that grabbing the rat there would somehow get the snake to accidentally nab the tongs, or something weird like that.