Reward multiplier applies to both, so yeah, flying low tier earns you shit.
Whats the best way to make silver? I don't know, I would say this: stop torping ships, don't destroy bases/airfields or anything like that because it ain't worth shit. The most amount of money i ever made apart from shooting down airplanes was bombing stuff with Wellington using 4000 pound bomb, on some maps you can nuke "packs" of medium tanks (like on Stalingrad winter, i think) and with good drop you can kill like 6-7 of them, each worth around 1k silver, then finish off the round flying fighters and you should get some nice money.Sadly stupid economy is still broken because of the stupid "upgrades" (not as much as before). You could also try flying Me410/U4, 150% reward means each kill is worth 1.8k
I think we should do some research on it or something, thats actually quite interesting, what is profitable and what is not.