I wished I had a solution for you, but welcome to the world of not listening. Seems Entegra and Thetford, with their Aria II Deluxe, have taken it upon themselves to protect you from maxing out you black tank while dry camping.
There is a flow adjustment that will increase the auto amount in the toilet, but I haven't found it. Techs tell me it is in that position.
So that said, I have seen about a 30% fluctuation based upon different park water pressures. Beyond that, you're stuck with using the "add" button (that's what they tell me) when it is "#2 time". If you are in a max rush, stow a brush like your S&B.
I'd tell you what kind of _____ proposition this is, but it is against forum rules to use that description, aptly applied