Please read this link www.usedwesterntack.co.uk/about/about-saddle-fit
It explains about saddle fit further. Seat size is solely for the rider, nothing to do with the fit for the horse. Skirt length is another factor of fit. Western saddle fit depends on 4 main factors:
- Bar angle
- Gullet width
- Rock in tree
- Skirt length.
Click Images to enlarge.
Example of bar angle. The angle of the bar (tree), should follow the angle of the horses shoulder. This is a example of a good bar angle.
This is a example of a bad bar angle, you can see the saddle is sitting perched rather than follow the angle of the horses shoulder
Example of back shape. The top horse has a straighter back with some wither. They Would require a straighter tree. The horse at the bottom has a curve to there back (typical of native and cob types). They would require a tree which has some rock so it follows the curve in there back and doesn’t bridge or cause pressure points
If your horse has dips behind the scapula (the area marked with yellow in this example). Then even a well fitting saddle will fall down into these dips. The only way to get that muscle to return is to use a ortho pad or shim pad with your saddle to stop it falling into these dips until the muscle returns. I see this more than I would like too, often caused by ill fitting saddles although can be caused by old age, cushions etc
Ortho pad can be purchased here: thewesternshop.com/collections/saddle-pads-blankets/products/professionals-choice-anza-smx-air-ride-western-orthosport-pad