Joel,
When I'm having zone problems, I make sure to setup with my line of sight at top inside corner of the zone, then look for a visual reference for the lower outside, usually the catcher's knee. Then I visualize a window frame around that box. If the ball breaks the window it's a strike.
As far as concentration goes, a question: Do you use a clicker to count balls and strikes? If you do, and you find you're concentration waning in a blowout, try sticking your clicker in your pocket and do the inning without it. You'll be surprized at how much your concentration picks up. (Of course if you don't use a clicker, this won't help.
)
-- Sam