I'm not sure how Bright does it, but in general the way most firms do it is off of a high watermark so that there is no over charging. If for example you made 10k the first month and 2k was taken out and then lost 10k and the following month made the 10k back, you are still in the same capital position but if any % was taken out the 3rd month then you would have had to give up a % on capital that was yours already.