The plate is 17" wide. Divide it into half and throw to one-half of the half plus the quadrent of the hitter. Those guys are good enough to do that. Even if their stuff moves off the plate it's good enough that most hitters won't hit it. Key idea: you don't have to hit the black every time---just as a tennis player doesn't have to hit the lines to win a point.
And that's how I'd explain it.
Rem