My opinion: No Tension at all!
FWIW,
all me experience points to NO TENSION at all in any STB.
Its purpose is to keep the upper of the strut towers at the stock position and not allow them to flex, eiyther INWARDS or OUTWARDS!
So, put it on, adjust the tension so that the bar makes solid contact with both towers and remains steady between them and then tighten the nout on the strut towers.
DO not tighten it so it pulls the towers inwards, do not tighten them so it pushes the towers outward.
By the way, if you put down some simple physics equations, you will see that the strut towers receive a lot more outward pressure when cornering than inward from hitting bumps or whatever.
Chris