So you're paying 0.0013 BTC but 0.0010 BTC has to be sent back for mixing? Does the participant then get the 0.0010 BTC again after mixing?
4.9% fee is outrageous, that's my free honest review for you.
For free mixing, network free may apply. Usually, participants will use their own BTC address during mixing, so the amount remains after mixing will reward for the participants. Any additional reward will not be sent to the participant for this review campaign. Thanks for point out that issue.