Gimbelock, when you do a static balancing for lateral balance, instead of holding the prop and estimating 90 degrees, try removing the prop entirely. Place the prop shaft on a table to support the nose end and then hold the plane by the tip of the tail (not the rudder). This will be more accurate. Of course, flight testing is always required to fine tune the lateral balance.
Like has been said, they need what they need. My Skybolt needed 2 1/2 ounces in the left wingtips even though the wings balanced individually. Likely due to the side mounted OS 1.20 FS.
Dave