Unless you exit before your Series A, which seems to be fairly common for YC companies: Reddit, Clickpass, Auctomatic come to mind... 6% at that early a stage might still be pretty high.
If you exit before your Series A, you're probably pretty happy anyway. I dunno about you, but for me I don't care if I get $5M or $4.7M, I'd just be freaking glad to have a few million.