Just my opinion for what its worth but i would have thought that the strut brace should be fitted with both wheels on the ground. reason being that when u jack the car up under the xmember, u are distributing the load through one point, a force that is never going to be replicated on the road & resulting in a certain (small) amount of flex to the inner guards. this could be the resultant 16mm difference u are experiencing. any other views?