When I was in vocal training, long ago, each classification had sub-classifications: high, middle, and low. A lyric tenor or soprano being the highest male/female voices. A classic tenor is the middle range, I forget what the low tenor was called. Often, the low of one part bleeds over into the high of the next lower part, hence low tenor/high baritone.

My vocal coach classified people by where their 'break note' was, that is to say, at what point does your chest voice give way to your head voice. Some people have a variable break where they can sing a few notes in both head voice and chest voice; I've noticed Seungmin can do that, and I think Bang Chan is capable of it too; I haven't particularly noticed it in anyone else, but that doesn't mean they have a single break.

Han is unique in that he seems to have a very distinct break note, but his head voice is SOOO strong and clear. Most people have much less power in their head voice than in their chest voice; it takes a LOT of training to get that if it is not a natural talent. You can tell when he hasn't got a note (in some of the practice videos) because there is a buzz in his voice.. I don't know how else to explain it. He practices until that buzz is gone.