have been googling 'the collapsed hip' and I think that's it, my weight drops almost entirely into my right heel - it's only since riding another horse more often that I've discovered I am the reason the pony's saddle slides slowly down his right side
since I do the same thing to something similarly fat shaped. In fact the only one I don't actually slide off after half an hour or so is my own high-withered one.
am pretty sure I never used to ride like this, so why has it happened and what can I do about it? am a freak :(