I am currently trying a Crates Melita Brown saddle. Love how it frees up my horses shoulders and she seems very relaxed in it. I have only ridden twice in it but both times the hair is ruffled on her back.  Keep in mind my horse is built down hill and I chose the Melita because it has some rock to it.

Both times I rode in a Thinline pad, 2 different ones. The first time I used the gray felt Thinline, no shims. Hair was ruffled on both sides. Second time I used a different Thinline, this one has the booster shim and the bridging shim (this set up is used under my treeless) one side was ruffled more then the other. I did notice saddle movement.

Can this be fixed with a different pad, or is it that it just plain doesn't fit?

I am not familiar with a booster shim but have you tried a wither relief pad or something built up in the front to level her off? Mine was real downhill her 3 year old year and has mostly leveled off but still a smidge downhill. Those helped me while we were going through that phase so may help you?

I get more worried about the ruffling than dry spots...

The booster shim runs the full length of the pad. It gives extra protection.

I have not tried something built up. I would think that would cause the saddle to bridge more but maybe since the tree in this saddle had some rock along with shoulder flare it may help. I will have to borrow one to see.

Try pulling the saddle more forward before you start riding.  I have a mare that is built downhill as well, and she also has a pretty straight shoulder, which makes the rigging position on alot of saddles too far back for her, therefore causing the saddle to want to work forward when riding.  Most saddles are rigged in the 7/8 position and with horses like mine, the full positiong is better due to how they're made.  A saddle with alot of rock to the tree is designed to sit more forward on a horse's back, almost up on the shoulder (like a Caldwell).  The rub marks you're seeing are from the saddle trying to fight forward when riding.  Move the saddle forward and I would bet that lessens.  

Thanks so much for the info! I actually tried it again without all the shims in the pad. It seemed better but was bridging. Then I put the bridging shim in and rode this for a barrel race on Sunday. The saddle slipped all over the place (yes my girth was tight). Soooooo I have decided to sell the saddle (Meleta Brown) and stick to a treeless for now....even tho I don't really like riding in one.

Check out About the Horse for saddle fit info and shim options. 

http://www.aboutthehorse.com/secure-web/html/videopadorderform.shtml

Thank you...I'll check it out!