i always put down the blue black tinter from my lechler scheme as a ground coat for colours like this, otherwise the coverage is just atrocious

i think if u had waterbased base coat, it would be fairly obvious, for starters if you're knocking back the basecoat as u say, the water from wet flatting would just wash the basecoat off lol. plus, he would have been sold the waterbased specific thinner, which is pretty damn obviously different to a standard 2k thinner