Yea, I edited my post since that isn't how it works now. When I first noticed it, I did some testing and got a pretty consistent 33% of the current hourly earning. Yesterday, it seems to have changed to be based on your max hourly earnings. This is a very positive change.
I tried a couple different girls, but my rewards seem to be the same.
It's a new feature. I wouldn't be surprised if they tweak it again if they think there is a problem.