Perhaps we just need to check for instanceof ElevationComparatorSource?
I had tried that, but it wasn't working - flipping them all helped make tests pass coincidently. A little more testing added and it fell down.
Latest patch reverses the QEC comparator, uses reverse=true for the QEC sort fields and doesn't require the distributedProcess part.
There is still a problem in the the QEC sort field used is 'id' - this causes a problem with distrib. If you change it to something like "elevate" that solves the distrib problem - but then some of the single node tests fail.
For now its left at 'id' and sorting by id in distrib with QEC is not supported iwth this patch.