Re: Okay. I admit it. I'm dumb!
Diagram is confusing. Have made the feeder and I like it.
Bees enter in a 3/4 slot the width of the feeder between the two "Bs", at the bottom.
They crawl over the top of the B board and feed in the V screen between A and B. The V screen extends the width of the slot A-B and must be tight to the ends. I stapled it to the top inside of A and top of B. V is formed from top inside of A down to bottom of tank and then up to inside top of B. Fold screen over top of B and staple.
Then staple on a piece of screen that spans from A to A.
I highly recommend a good coat of beeeswax on bottom and walls of tank before As are installed. Seals corners and prevents molding on the sides. I also used silicone on all wood to wood seems as I assembled, as leakage can be an issue.
As you can see from the attached pics, I made a simple 2x4 frame and attached a 3/4 plywood to the under side and then cut a slot with a jigsaw.
Zone 3b. If you always do what you always did, you'll always get what you always got!