Wintec's don't fit every horse, in fact that fit very few. Generally fat, round ponies without massive withers.
Try getting a saddle fitter out, they may be able to add some packing so have it sit better. Unfortunately I don't think there is a great deal that can be done here though, new saddle may be the way to go. You can pick up second hand, good quality saddles for pretty cheap on Ebay
and some saddleries.
I would try a Kieffer - they tend to be good for high withered horses as the pommel is cut back.