Never feel obligated to tip more than standard.
Always tip what it was worth.
Example, I once got a bbbj but no kissing or daty, so I only left 40 which I felt was more than fair and she didn't seem at all displeased, in fact said ooouh when I pulled out the second twenty, so maybe 20 would've been enough in that case.
They already are getting your door fee which would be enough at other places, albeit lower grade eye candy. I'm thinking if I repeat with a girl enough, all those door fees should aggregate a surplus for her to give a little leeway in the tip department.