Saddle fit tips

[Deborah Haney]

Max wore his little pack on a walk for the first time today, just a loop around the park across the street. He did really well but I couldn't figure out why the saddle kept sliding to the right, especially when he trotted. The two rolls that were supposed to rest on his ribs kept pinching together and resting on his spine together; is that okay? I adjusted the cinch so that I could just barely slip my fingers underneath. The pack was empty. Does anyone have any tips for how a saddle should fit properly?