I think you have a relatively shorter torso and relatively longer legs. It is also possible, if you lack flexibility in the back, that you might tend to sit up straight. Either or both of those could make your body try to shorten the distance from hips to hands. Which means either shifting forward on the saddle, or riding with hands on the tops. Also, if your seat is a bit too high, your hips may be shifting forward in order to shorten the distance from hips to pedals.

Maybe you can experiment with those things - fore and aft position of the saddle (using a different post without so much set back), position of hands on the bars (eventually maybe a shorter stem), and lowering the seat just a bit (like 1/2 cm).