Can't help so much with the overall profile issue, but I can assure you .20" is not likely too small of a gap. I'm fitting my 10 cowl now and the plans call out 1/8" spacers taped to the cowl front in 3 places to give the offset behind the spinner.
0.125" spacers plus a ply of Gorilla Tape securing them is less than .2" thickness - so if the idea generalizes to the -6, you're good to go. I could go measure the gap on my -6A but I'm at work.
I'm not sure there's much you can easily do to profile the cowl to the spinner, going smaller, because of the honeycomb.
Cowl fitment underway last night with 1/8" spacers taped in place behind spinner:
Hop-Along Aerodrome (12VA)
RV-6A - N30YD - Built '98 / sold '20
RV-10 - N130YD reserved - under construction
donating monthly to the VAF - thanks, Doug