This is why I've always been an advocate of practicing with the crosshair turned off. cl_crosshair 0 is the command, I think. I used to play at least 1 hour of deathmatch every day without a crosshair, using usp/glock only (or sometimes a deagle). Or definitely if I was pubbing I would turn it off. You shouldn't be relying on it, it should be intuition. You shouldn't waste time and mental energy worrying about lining up the dot on a guy's head, that should be second nature.
You really shouldn't need a crosshair at all for close/medium range, and at long range the tiny dot is obviously much more helpful than a big crosshair.
Just my take on it. Small crosshair all the way IMO!
Fill me in here because I don't see it adding up.