Not sure of exactly how your set up is, but, have you put the belt into the V of both pulleys first and then ease the back of the belt onto the tensioner wheel? My tesioner is flat faced and works agains the outside of the belt. If I put my belt over the tensioner 1st I know it will not go over the pulleys and into the v slot.
Good luck and hope to see you one day.
S7MAD