Join Date: Dec 2010
Location: southern Arizona
There are two parts to the fit of the front of the saddle. One is the angle of the bars. Think inverted V. If the angle is too wide, the front of the saddle goes lower and there is uneven pressure on the tree. If the V is too narrow, the ends will gouge into the shoulder while lifting the front higher.
The angle ideally should be the same as the horse. If in doubt, wide (and low) hurts less.
Also, there is the horizontal distance - 6.5, 7 inches etc horizontally between the bars of the tree. Again, too narrow will raise the front, and also gouge. Too wide will lower the front, but then come to rest. If this is the case, a wither pad (or folded towel) will help. I sometimes use one because my Arabians have wide angles, but narrow horizontal distance. A wither pad fills in the gap. With a western saddle, and with a felt pad & Navajo blanket underneath anyways, it doesn't seem to have any ill effect on the horse. With an English saddle, and a very thin pad, that isn't true.
Look to see if the angle of the saddle matches your horse. If so, and the saddle rides low, it probably just needs some padding. I used to use a fleece wither pad from Statelinetack ($8, IIRC), but now will use a folded wool pony blanket (the blanket is 24x24, so folding it makes it 12" wide, and each side hangs down 12" below the withers). You can try a thick towel folded, and see if it helps. If it doesn't, there is no reason to try the wither pad.