Regarding belt tension, I don’t see a recommendation for the newer 9mm belts. The video must be assuming a small SO3, not the XXL which weighs factors more (using the “lift one side of the machine with the belt” approach).
My primary goal here, after seeing significant inconsistency, is to FIRST achieve CONSISTENCY, FOLLOWED by ACCURACY. If I can get to a consistent +/- 0.01 then I will be pleased. If I can cut that in half, I will be happy. If I can cut that by 2/3, then I will be ecstatic.