I agree with maddafinga.
I used to use brand name flat finishes, but on heavily weathered aircraft, it still looked to 'satin' in appearance, hence didn't look 'right'.
I made up my own flat finish, and it works like a charm.
Tamiya flat base
Future floor polish
Windex
I dont have ratios, I make a new batch every time I run out, and because you never know when a manufacturer might change their recipe I have chosen to not risk it, and spend a few more minutes mixing, rather than a few hours undoing a total stuff up.
Yes I agree, I have trust issues