The seat base tilt is not adjustable like it is on other BMW's. As others have noticed, the front of the seat is too low. For me, raising the height 7/16 inch was just right.
I designed some front and rear rail spacers with the right taper to do this. The spacers duplicate the stock rail floor contact areas. We made them out of black Delrin to blend in. We also made some new cap nuts (316 stainless), similar to the motorsport strut brace ones. This let us use the stock front mounting stud. Will be making some Delrin caps for these similar to the ones used in the E36 cars.