I have had several "experts" tell me that when this happens, the saddle *doesn't*
fit. Shatirr has this uneven shoulder problem and changing pads, using shims etc
didn't help for endurance. He wouldn't show the rubbing untill June or July, but
he was very tender there even when the hair wasn't rubbed away. Shims are one
option you can try, but they didn't work, over distance, for me.
What did work was changing saddles. I got and SR Enduro that worked great for a
while, but I had to re-adjust it if I let his condition change dramatically, like
3 months off in the winter and then riding alot in the summer. The easiest is the
SS endurance model. My Kiefer Wien dressage saddle cleared his shoulders nicely,
so a dressage saddle might be an option, but many don't have adequate bar width
for distance use.
I'm getting the SR fit to Kadance for the coming season, and will use just the
Sport on Shatirr.
Good Luck!
Linda