(No pictures unfortunately...)
I've been leasing an appendix mare for a few weeks now, using the owner's saddle because mine had been in storage. Her saddle is far too small for my rump, so I stopped being lazy and got mine out of storage and used it when I rode yesterday. The fit seemed fine, even, no rocking forward or back, and she expressed no signs of discomfort; in fact, she's usually grumpy about having the girth tightened (not bad but visibly irritated) but yesterday she only flicked her ears like she was waiting for it to be uncomfortable but it didn't happen. (She was uncharacteristically fidgety with her head however, almost like she had an itch, and seemed itchy when I bridled her.) She has white spots on her withers, so clearly she's had an illfitting saddle, possibly the owner's current saddle.
I rode her, she was as good as she always is - but she is a very well trained horse so I'm not sure if a poor saddle fit would manifest in her behavior. After her characteristic initial laziness she was ready to work other than wanting to avoid a certain spot in the arena for some reason but we worked through that. Rode for about 35 minutes then unsaddled her then inspected her back. The sweat pattern was even, but then I noticed a small bald spot right on the top of her withers.
I can't for the life of me remember if that was there prior to saddling her. I am short, and her withers are taller than my head, I barely glimpsed it on tip-toe. So I feel like I could've missed this when saddling but I don't want to ride her in my saddle again if it is the cause. It seemed like, almost, an old bald spot? It was not red, or irritated looking, it was white, almost like an old scar white. But when I touched any point of her withers, as well as the spot, she swished her tail and fidgeted. My pad is heavily fleeced at the withers, could that have done it? Or does my saddle just not fit? I know you could tell better if I had pics, but I didn't think to take any when I tacked her up because the fit seemed fine to me. Now I wish I had.