That's correct. The math is confusing and why they have to do it this way is beyond me,
8:4 = 2:1, 8:8 = 1:1
Freddy is right on as "something" is wrong with the gun or air supply if you can only get a 5" fan even with the 2:1 ratio. Nason's metallic line is a PITA to use and their Silver is about the worst. I use their large flake metallic under kandy graphic's which is pretty but it takes some "adjusting" with the mix & gun to lay it out right. I've tried the 1:1 mix and it just doesn't spray well for ME, so I've just learned how I can use it best for ME and I seldom need a drop coat unless it's just a "bad" day.
I don't know what the "recommended" pressure for that gun is,but I'd bump it up 10 psi or so and try that. Silver needs a little extra sometimes to atomize it.