I understand why not to, but having trouble figuring out how not to. I've done 15 or so road and crit races (albeit Cat 5 and 4/5) over the last two years and I have yet to be in a race where the pack wasn't massively overlapping wheels. Only when the front is hammering to we end up in 1, 2 or even 3 parallel lines of non overlapping wheels.
I tend not to overlap and close gaps/keep it tight, but it [seems that] most of the riders around me half wheel it and then muscle over. It seems like like the only way to protect your position is to half wheel it yourself.
[edit - meant to say that while I don't overlap, it do work hard to close gaps and ride close to the rider ahead of me.]