It's had to tell from the pics (the angle, the horse not being square etc) but to me, it looks like the balance of the saddle is a bit off. Do you find youself pushed back into more of a chair seat when riding in it?
Your horse's wither doesn't look super high and narrow, it just looks like a normal tb wither. You may not get the same clearance over the wither that you would with a horse with a smaller wither. I have 2 fingers clearance over my TB's wither in my saddle. I questioned my saddle fitter and she said that with TB's its a normal problem.
You really need to be careful with gullet sizes though. You want to make sure it fits here, and doesn't dig into the Trapezius, Lattissimuss Dorsi and Serratus Ventralis, not just over the wither. Capture.jpg
If it's too tight behind the Scapula then a few problems can arise...
Potential Muscle Damage, Myofascial Trigger Points, Reduced range of movement to the shoulder & full extension of the foreleg will be impeeded, horse may become "girthy" or "cold backed" and it could also create referred pain down the girth line, into the lower part of the neck, back and hind quarters. I am an Equine Bowen Therapist and see a lot of these issues when working with horses, some cause by other things but mostly caused by saddle fit.
Putting a pad on can also increase the pressure... Like putting on 2 pairs of thick socks while wearing shoes that are a size too small. There is less space between the hard metal of the gullet and the horses soft tissue due to the extra padding.
I would get a saddle fitter out to have a look at it... As I said before, from the angle of the pic, the balance of the saddle looks out and also the fitter will be able to advise on gullet size and padding for the saddle :)