My opinions ....
You don't need the switch on the SC heater. It has a thermal cutout so at most it helps on the startup and has no impact at roasting temps. I've done it doth ways - no significant diff.
6" off the TO is likely too much space. It's pretty common to use a springform pan ring (~2.5 inches high) on the GG.
Try preheating for a couple minutes, then continue at full power till 1st crack, at least till you are convinced you can get to 1C handily.
1465W should be enough, tho' I've always used the 1450W Galloping Gourmet. You can't afford to blow out all that hot air - make the system reasonably tight.
I believe the sweet spot on my GG based SC/TO is 350 grams of greens. ~12.5 oz. Too much and you get a too-slow roast, too little and you get a fast uneven roast.
Seems like you addressed most of these and still - no joy !