I lay out where I want the apex of my rails to be with colorful permanent marker - Sharpie - in red/blue/orange/yellow, etc. I use different colors for different things. I may end up with pencil holes w/ink in 'em, at certain points for my laying out process, and blending my rail apex from 30/70 - 50/50 - 30/70.
And, I write all that to write this, I feel some validation when I read Mike D. say there should be some paint left… I always end up with some ink left.
After all the crap I talked about an art professor I had who ripped a couple guys new ones for not “finishing” their work enough, then to see her show with completely “unfinished” objects… Anyway, I find some satisfaction practicing the kooky motif of letting “the process” show. But, that’s a different story…
To get back to the topic, I agree with what everyone said. I’m still in the flat deck, round rail camp. My “bands” are more like passes to take away foam I know shouldn’t be there… I visualize the curve I want and take it from there.