When I heat up (expand) the stainless bands and set then on the rotors, I actually try to get them to be offset slightly towards the inside of the alternator. If you were to measure the inside depth of the band from the inside of the rotor, the depth would be slightly over .5". This is  enough so that when they are poured and the cover goes on, it doesn't quite touch the magnet face. This causes a layer of epoxy over the inner face of the magnet. I feel this seals everything in and tends to make a more weather tight seal so there is not any corrosion problems later on.