I don't quite remember the reasoning behind the theory. Keep in mind, it is a theory so use it as just that if you like. I read a long thread on Elite one day about it. Well, maybe it was CarSound. I don't remember, but it was LONG and CONFUSING. As far as the end correction, you use the height or the smaller number of the two ie. 1"x15". That would be 1" high x 15" wide. So you'd add .5". Or you could theroretically look at it on a vertical note as 15"H x 1"W. In that case you still would use the 1" measurement. Just remember, it's always the smaller number. If equal, well, that's a no-brainer.