put a pen/pencil across the seat and see where it settles. If it’s behind center, the saddle is too narrow, or sitting too far forward.
Wither clearance doesn’t tell you anything about the fit, other than whether it’s going to start squishing the withers. A pommel will have more clearance on a low-withered horse than a taller-withered one, all else equal. This saddle looks to have what I call a “cathedral pommel”, meaning quite tall, which makes it suitable for horses with giant withers. That alone doesn’t mean the addle doesn’t fit, as wither clearance is only part of the fit. It’s really not possible to tell how well this saddle fits.
We’d need a rear view to see how it fits across the back - channel clearance and panel shape- a 3/4 front view showing all the shoulder and saddle, and a side view where you’re a few steps to the center of the horse instead of closer to the shoulder, for a more straight-on perspective.
The saddle should be girthed, but no pad
Place the saddle up high, close your eyes, and slide it back until it “sticks”. That’s where that saddle will sit, and that’s where you gauge fit