Actually Kenster, 20 highs aren't the same foot print as a 10. They are the same foot print as a 15 and a 30 high. 12 inches by 24 inches.

Unless of course you are talking about a 20 super show. That and a 15 show are great tanks to display angelfish and discus, but surely I digress.
You are right in the theory though. A long tank, 20 gallons or larger is necessary for an adult corn. If an adult corn is 60 inches long, then half of that of course is 30 (the length of a 20 long). The snake could in theory stretch out around the perimeter of the tank without its head touching its tail.
<------------------------------------------> 30 inches
^.........................................................^
|...........................................................|
12 inches.......................................12 inches
|...........................................................|
|...........................................................|
<------------------------------------------> 30 inches
So overall the snake has a max of 84 inches to stretch out. That's not really a whole lot of room considering it doesn't have another half of its body length in free room.
This went all off the deep end. Hope it made the least bit of sense. Time to go to bed!
Peter