I think part of this answer relates to the snake's psychology as opposed to physiology. I believe hatchlings and shy yearlings and subadults should be kept in compact quarters. They feel more secure and less stressed. Physically, I think established snakes should be in an enclosure at least 2/3 as long as the snake, e.g., a 10 gal, 20 inch long viv will accommodate up to a 30 inch long snake. A 20 gal long, 30 inch long will serve most adults 45 inches and smaller.
I do think snakes benefit from some room to roam once they feel secure in their enclosure and, personally, I like a larger glass front viv that lets me enjoy looking at my beauties during the few hours when they decide to explore their home. And although all the experts say corns spend most of their time on the ground, I find a little bit of head room is thouroughly exploited. All my snakes like to climb the branches and plants in their respective vivs.