I hate to say I don't really have anything enlightening to say about it; it's really just personal experience! I think probably some other folks on this forum may more eloquently be able to articulate reasons for this. Not to mention, I'm sure a lot of people would totally disagree with what I wrote; through a long journey of tone, I just found that small cabs just have something special about them I can't name, and a lot of times, to my ears (I have to stress this is the most subjective thing in the world!) when it comes to mic'd sounds, the smaller cabs just sound bigger sonically. I know that doesn't really help, sorry. I'm not professional either, by the way. To investigate this, just work with some random factory cabs that are small and fool around until you get the character you want, then compare with some 4 x 12s. To me, usually the top end and pick attack on mic'd 4 x 12 often get thin. Maybe it's just my guitar, my pick, my pickups...who knows haha.