I spent over two years punting £150 Thai girls every week. I never once even thought about giving a cash tip, but I did occasionally buy silly little gifts for regulars and they often reciprocated. I can see two as I write this, and it makes me smile.
I still have that £150 figure in my mind as my "budget" and so now, if I get fantastic service from an £80 Pole or Hungarian, then I have been known to slip her an extra £20 on the way out. It doesn't happen very often!
Flame to your hearts content, but I sleep well at night.