Another remark without understanding acoustics........I love it. Yes, most of the audio community will measure centerline, but this completely disregards the high pressure at the bend, therefore without using 45s to control the propagation of the wave, the high pressure area HAS TO BE COUNTED!! The measurement was not exterior, it subtracted the thickness of the wood. . If he were to put 45s in the line, then yes, a centerline measurement would be recommended. You cannot disregard the portion that causes the most effect in the output in terms of nulls and peaks. A lot of people do not know HOW to account for this, so they go simple.
Do you understand now?