It's worked well for me over about quarter million miles and 20 different bikes.
You really think when it come down to millimeters on belt tension that 7 vs. 9 is gonna put a mushroom cloud over your bike?
The bandwidth between too tight and too loose is about 1/2" IMO. 5-7mm is on the cusp of too tight to me. All the HD's I've ever owned were on the order of 3/4" minimum and they've had belts since the early 90's. I guess it ultimately boils down to the pivot angle of the swingarm compared to the pulley centerline and whether or not the axle is moving away from the front pulley during shock actuation or towards. With HD's, it's moving away until a certain point, then back towards, but only at suspension ranges that bottom out most shocks. I should check this on my VStar.