Set your chain tension with the front sprocket, swingarm pivot and rear axle in line. This is as tight as it will ever get so give it a little bit of slack. 10-15mm should be fine.
Rather than a spring loaded tensioner fit a roller from a late model bike. The roller should go as close to under the swingarm pivot as possible and you set the position, height wise, by again locating the sprockets and swingarm pivot in line and putting the roller up until it just touches the chain. There is room on the swingarm mounting plate on an XT/TT frame to accommodate this. Once it is set the chain tension will hardly vary it should hopefully clear the bend of the swingarm.
Since the end of Village photos I need to up load the photos of my set up again. I’ll post them when I get time.