Hi David
could this maybe be beacuse of mutiple lobes on the oversize antenna and with them having a high angle of radiation? hence the better reflections
I found this in the past on two meters I got much better reflections on my 12 ele beam when its clamp wore through the fibreglass stub mast and it tilted upwards, all of a sudden i was getting much better
pings and refelections on the band.I am am no antenna expert but that is how i would inturprete the good results.