I'd say bring it back to the factory settings and work your way from there. Try to tune it a bit with the wheels elevated and not on the track because (at least for me) it's hard to see how much smoke is there when it gets too far away. I usually try to tune the low-end and idle first, then work on the top, others might disagree. I also use a few different observation methods to check the tune.

I'll check to see if it has smoke all the way up to the high rpm points, if not, too lean on top.

check to see how long it takes to drop rpms after it's a full throttle for few seconds. Should stay up for about 20-30 seconds before it starts to bog.

I also check the idle by again having it elevated and seeing if my rpms are steady after opening and closing the throttle. I'll hit the brakes, and back to neutral. If it starts to spin the wheels again, I back the idle out a bit.

I agree it's hard to help without being there, but the C6 was my first successful tune as I just started this last year. Mine always started out rich on the track but by lap 3 it was at perfect tune almost and as the mains got longer, it held it's tune all the way.

Hope this helped.