I'm pretty sure that the further out you go with the mixture screw, the richer the mixture gets. Glider can verify for us, but I'm 95% sure.
(it's the other 5% I'm worried about)
You're correct, you're adding more fuel the more you open it up. If you go more than 3 or so turns open, you need a bigger low speed jet and stand the chance of the idle mixture screw working out on it's own and loosing it.