I get the feeling I use less shampoo than most foamgun users. I do it by eye and I'm certainly not precise about it. I use Griot's Car Wash and I have a pump dispenser on the gallon jug. I take a second (empty) gallon jug and put in some water, maybe a pint's worth. Then I pump about four-six pumps of shampoo in, shake it lightly, and fill it the rest of the way with water. This might be different from what I've posted previously but it's what I did last night when I mixed some up.
I fill the guns from this jug. I generally use the next-to-smallest setting but I'll bump it up to a stronger mix when doing dirtier panels. But note that I still keep my mitts in a bucket of wash solution when washing, generally filling them with it by holding the cuff open and the mitt under "water". I still use the two-bucket method when using foamguns.
When I'm using the mitt-balloon method I use a slightly stronger setting, about the middle of the mixing bar. When I spray the foam through a BHB, for cleaning really dirty areas, I use a pretty strong mix setting.
The only problems from using a strong mix would be cost and LSP stripping. If your LSP holds up OK then do whatever you like doing; if your LSPs need redone more often then dial it back a bit. The more shampoo, presumably the greater lubricity/protection *and* cleaning but there's a limit to what most LSPs will tolerate. And it always pays to find a good LSP/shampoo combo.