Yea, you're right. I guess you would have to assume an Ace or King will win with top pair on this board.

So, I'll rework my math to solidify my thinking:
He's only about a 25% to hit his hand, so he loses 4.20 3 times (12.60), and win 8.25 once (don't forget about the blinds). Overall, that's -EV of 4.35, or 1.09 per hand.

For this to be +EV, the he could call no more than about 1.25, right?

FWIW, If I'm right, I just plugged a big hole in my game, both for calling down the flush draw, and giving my ops proper odds to call.