Its likely that came from multi-path issues with the smaller capture area on the Jack. When I did those original tests, I lowered the mast a tad and also moved the RV back and forth to make sure I wasn't getting bad measurments, but that same thing happens at the house on the very few stations I can see OTA.. :(
BTW- I have never seen mfgr. specs on either antenna, nor was I able to get any information whatsoever from either Winegard or King. That makes ir easy to claim whatever you want but reference it to nothing.