Originally Posted by stoneage
I don't think it is strange that they behave differently since they describe different things. The curve describes a swing, admittedly a very simplified and crude swing, but a least a swing where you apply a force to the racquet. MgR/I describes what happens when you attach the racquet to a cuckoo clock.
You can find other placements of the weight that might change the curve, but not MgR/I. For example you can add 10 kg at the but end or at a point around 48 cm without changing MgR/I.
That is probably why MgR/I isn't a personal ideal number, but differs with different weightdistributions.