I blasted full-time for years as a job. My advise is to use a sander first, then do as little blasting as possible, then more sanding. My thoughts are that blasting moves the metal around. I'm doing a rusty 37 car and I want as little as warping as possible. The one person said at a 45 degree angle which is very good advise.
If you use a blaster first, you then usually get to carried away. You waste sand and cause warping.