GROUP AS payload not correctly included in spilled map element sizes

When appending to the GROUP AS payload array we account for the increased size in the total size of the group's map, but not in the individual element sizes.  This means that when spilled/restored we're not correctly accounting for the size.  This leaves us with an inflated total which is the basis for further spilling - and we end up using a large number of tiny spill files, which we shouldn't be doing.  By correctly accounting for the adjusted size in the individual elements we remove the impediment to the correct functioning of the spill logic.