Then we’d feel more like home, as “luft” is all you hear here, never zrak. But we have that all because of historic and other reasons …

Well, kozarec is the standard language form, glaž is what you’ll mostly hear (at least here), but kupica is an exclusively archaic word. You can come across it only in folk songs and such, noone actually uses it. Though I think it is present in Croatian, even in Kajkavian, isn’t it? I have definetly heard it from them before.

Kupica is still present in kajkavian,especially in Zagorje.