Yep, that has to be a rewarding feeling.
I'm attempting to duplicate your chart work, and so far I come up with a Channel Width of 39 and change...... twice what you are working with..........Admittedly however, my work is not without constant interruption as wifey is bugging me to help get ready for overnight guests. I think I need to find a refresher course for the "channel" drawing............. I'll be looking at it again tomorrow. In the meantime, guess I better get busy (with my domestic chores).
EDIT: Decided one more attempt to understand how to draw the channel.........Got it.......
EDIT 2: I didn't realize my channel height is same as what you are using, so I removed my prior comment about having a "rounding error"............ I'm cool now with your illustration.........I think