Mikrotik HTB-Token Bucket Algorithm After 6.35
You can find the wiki article here.
The HTB system is a little wacky, and recently some previously hard-coded values are accessible for configuration, namely bucket size. It was previously hard coded to .1, but is now configurable from 0-10. Janis created a nifty diagram to help illustrate how everything works:
If this sort of thing is your bag, then jump in with both feet.