Well that's a good point. I've always assumed that you can't take any additional base edge off using a guide. If you file to a 1 degree using a 1 degree guide how can you got to a higher bevel?
this is also one reason I am using a .7 these days. I know I am ending up less then 1 degree and a .7 seems to have some advantage of a .5 with a liitle of the smoothness and forgivness of a 1.
I really bevel most folks who are tuning there own ski probably over bevel the base. it is very easy to do so.
Base bevel increases from skiing on hard snow after a period of time. Even though it may be a small amount base bevel is the heart & soul of a tune and very small changes make big changes in on snow performance.