What Jim said.
I'd do some test shots with the Ful-Thane. Depending on what color it is and adjust the ratio of reducer from that.I'm not talking a short 1'x1' panel,PAINT a piece about 2'x3' wide.
If it's a metallic or light color,I'd go with the heavier base ratio. Nason does not cover for crap so the more pigment you got,the better.