it shouldn't be a problem if a new belt has one tooth less. The diference should be taken away by tension roller.

"the crank moves a bit takin the slack of the belt before the cam gear moves, so the crank and cam gear are not both at TDC. (also tesioner is untightened 180 degrees)"
Move belt on one tooth over the cam gear here to eluminate this difference. just check that everything in TDC after you tight tension roller. If not make it one more tooth over until you get it right.