I would think that if the weight box is NOT in line with your CG, centrifugal force will try and get it there.
Depending where you located it on the tip rib, that could be detrimental to line tension, i.e.- placing it too far back on the rib might try and rotate the outboard wing fwd (LH yaw). Think of the tip weight as a small pendulum. Engine offset and/ or rudder offset would counter this effect, but why have two forces (no matter how minute) fighting eachother?
While I can agree with your statement, the practical arrangement seldom allows us to place the tip weight in a direct line from the center of the leadouts, through the CG, and to the outboard wingtip, which would be the best location.
So, we often make compromises, and placing the weight box as near as possible to the thickest portion of the wing, at the outboard tip, is one of them. This is even more of an issue when we use the traditional tip weight box.
Using a tube as Randy does is likely the better way, as weight location can be placed, easier, into the best location.
The moment arm, between the optimum location, and the thickest part of the wingtip, is very small, especially considering that the relationships change with changes in Cg, and leadout location during the trimming stages. It's all a set of compromises.