They have a really powerful pressure washer though, how much do you use per car. With 1-2inches of magifoam topped with warm water I'd use a third to half the bottle?
I get through the whole bottle no worries if its dirty!
I apply it "liberally" everywhere, including plenty under the arches and on the insides of the wheels and brake calipers and after a jet wash they're not far off perfectly clean
I can just about get away with half a bottle if its summer/recently been washed
I probably use less than a 10th of a 500ml bottle each wash - but I find if the ratio is too high or low then it doesn't foam properly. It took me a while to get the settings on the nozzle, pressure washer correct so that I got the right amount of 'sticky' foam.