OEM HD Plugs vs. Aftermarket plugs

When I bought this bike in stock trim I was getting 40MPG consistently, then I did a Stage 1 and mileage went up to 43MPG,pretty good I thought...then the hybrid conversion with a TW21 mileage stayed at 43MPG. So this year after listening to the hype that you must use stock OEM plugs because of the ion sensing gizmo in these EFI TC's I decided to try a set of OEM plugs....now I'm getting 48-49MPG
My riding style hasn't changed a bit...the only changes I made was to use OEM plugs and I went back to fossil oil....
So...it got me thinking(that's dangerous LOL)....could it be that, since the spark plugs are actually a sensor in the ion sensing device that with aftermarket plugs it is not throwing a code but is retarding timing a bit because the ion sensing is getting a different reading than using OEM plugs
My question first of all is.... If you retard your timing would you use more fuel??
I asked a buddy when I went to his shop for a inspection sticker about it and he said that the aftermarket plugs you can buy anywhere are mass produced and quality control is a little less with Champion RA8HC than the low production plugs Champion makes for HD

I'm at a loss to explain why this year my mileage jumped 5-6MPG's...could it be that Harley's claims about using only OEM plugs are valid???