If You remove and weight the whole recone kit intact You are in fact weighting full weight of the surround and spider. Only fraction of their weight should be taken in the calculation, because one edge of the surround and one edge of the spider are not moving.For the surround, we can assume that only halve of the weight contributes to the MMD. while for the spider it can be less than 1/2 because of the greater difference between inner and outer diameter.Therefore recone kit always weights more than MMD.