I looked on the internet but only found videos relating to on road belt tension. What I do, and I'm sure there are other/better way from doing it is this:
I come from the on road world.
What I had been taught is that you should tension the belt just enough so that it is not skipping under hard breaking or acceleration. Then, because one belt is longer than the other one and has a bigger stretch potential, you could make the longer belt slightly tighter to compensate if you feel that the front end (because the longer belt is to the front end...) is not quite in tune with the rear end when breaking or acceleration.
What I have been doing with my offroad belt cars (I previously owned Schumacher Cat SX3 and K1) is start with the same method, and then also look for belt skipping when landing after jumps. I also found that I had to redo the process once or twice after putting a new belt since it stretches a bit after a few uses. Also, I was taught to watch for wear on plastic pulleys since skipping belts will wear them quickly.
Hope it helps, even if it is not a video
Martin Paradis