When I painted my first Airfix Germans in our old shed, up until then I had never dreamed of actually painting them, I merely sloshed on some enamel paint and that was that, of course with use and being a soft plastic the paint covering didn't last all that long. It was years later after I had played my part in the downfall of communism and married that I got around to painting metal figures which didn't bend, apart from the spears or swords of course. Either my memory is worse than I think or they were not varnished either, but the paint stayed put much better than before. The paints were of course matt but many old hands still preferred to gloss varnish their figures with the hardest yacht varnish they could find, almost small arms proof.
I must have used Humbrol matt varnish as our only choice back in the day was Humbrol whatever. Then the market opened up as did the spread of information and I began to use Winsor & Newton Matt Acrylic Varnish and never looked back, until recently. W&N gave a kind of slight satin sheen to the figures, not entirely matt but close, I read that if you sat it in cupboard for 3,000 years until it separated you could tip some of the agent out and it became perfectly matt. Being married I didn't have thirty minutes to spare never mind 3,000 years so my troops wore satin.
Anyway I recently went back to brush varnish, again it was Army Painter and I followed the instructions, even constructing a machine to shake the bottle (see Eureka below). One or two guys were matt the others came out satin, I tried again with a different bunch and again I could see some parts really dull but the vast majority were satin. To make things worse the stuff on my painting palette dried ...... matt!
So where does that leave me, I now give them a coat of brush on, then finish them off with a spray, more hassle but perfect.