I want to know if the gullet (believe that's what it's called) touches my horse's withers, the saddle does not fit correctly, right? Thanks
Absolutely right. You do not want the underside of the gullet to touch or bump the withers when you ride. That will cause damage to the horse. Also be sure the channel(down the backbone) does not touch the spiny process either. These things mean the saddle tree is too wide for the horse.
Nancy, you should be able to get 4 fingers between the top of the gullet and your horse's withers. A saddle that hits his withers will cause him pain even if he doesn't show it. Putting a pad on to buffer it is not the solution.
If the saddle fits along his back, then a build-up pad will fill the space around his withers and lift the saddle up in the front. It does this from the sides not as a bumper between the top of the gullet and his withers.
My 1,100lb QH has that problem, he has narrow withers and a wide back. I have to use a built-up pad to help my saddle fit. I've tried over 1/2 a dozen saddles on him and that is the only solution that works. There is white hair on his withers indicative of ill fitting saddles hitting him, all done before I got him.
Sounds like your tree is wya to wide for your horse. You can cheat to a degree if the tree is to wide and you working on building that muscle up BUT if the saddle is sitting on there already, not sure you would be able to build enough and add use some good padding, enough to make it comfortable for your horse.