Usually have a 10% mark and a 20% on the mix cup.
I won't cut mine at all for initial priming and I use a 2.0 tip.
With the 1.8,which is "close" I'd do the 10% after catylizing and it ought to do fine and the build should be OK,Just don't bomb it on heavy trying to fill the well and let it flash off overnight after the 2nd coat.
Guide and block it with some 180 dry and hit it again same as before and you should have enough build to finish it out as long as the substrate was fairly "right". Guide,220 dry,guide,320 dry,grease & wax remover to SEE how the scratch looks and more wet if needed. Or a double gray scotch pad wet with some soapy water if it's close. I went to this gray pad wet lately and it's just a beautiful base to paint on. For what I'm worth.