Low fee is just for marketing purposes for now, it may increase in the near future. We have a lot of obfuscation inside about what i'll not going to tell here because of privacy purposes.
Its understandable you have to start on something that will attract mixer users when you are starting out in this business, and you did the right thing by offering lower fees and launching a marketing campaign, I'm sure your users will understand but it's much better if it's slightly lower than those fully established mixer.
But as long as you keep your reputation clean and very active here you can build loyal users, it's a long way but since you started right you just need to keep up.