There is a procedure for rotating the belt in the FSM. If the tensioner distance changes you might need to adjust if it is not in specification. The last one I installed I had to go back and adjust the tensioner. If not 4mm I try to be on the lower side of the spec which allows for more travel when the belt stretches. Also you need to check the bely deflection between the gears along with the tensioner gap. Sounds like you are almost there. Good luck