No debate here? "Would work fine for that purpose", if he wanted to loosen a stock set-up. BUT he's trying to tighten a non-stock set-up. You gotta read the whole thread my man...
Outthere ordered a 26T sprocket (Not stock 27). I have done the same thing and it made the belt way loose (IMO). I slotted the tensioner to act like an old V-belt adjustment and found it would loosen up no matter how tight I mounted it because there is clearance left in the slot when you are taking up slack instead of relieving slack like you did. My solution of the set screw worked perfectly at stock mounting bolt torque specs and was very easy to tighten to whatever you like to boot.
With Lunatics solution to his opposite problem, the tensioner is held in place by the end of the slots he made, would not need a set screw. Happy now?