“I am geometrically stupid”. Galina- what about me? I am mathematically challenged (not just geometry).
I think when covid is over or you and I get vaccinated, we shoukd ride out to see @JinMA’s art works in person.
Jim - thank you for the pics and the info. I love your choice of apple varieties. I need to convince my husband that my plan is well thought-out (not) 
I have a tree on b9, it is small, but i think I will manage to get few scions. But thanks anyway!
If my reckoning is correct, the last twelve feet come from the verticals on the ends. (But like I said, math is not really my strong suit.)
yes, i didn’t count verticals, do they also produce? I whish i can look at a picture of mature(5-7 years old ) Belgian fence in bloom.
My end trees are some of my least fully developed at this point, so I can’t say from experience, but my working assumption is that you can treat the “endposts” similar to a vertical cordon or spindle. My guess is that they might be somewhat less productive per foot than the diagonals, though, since the 45’ angle is supposed to be good for encouraging fruit-bearing. I guess I’ll find out!
Also, I’ve seen that some people train the scaffolds horizontal at the top, so that they form a kind of top rail to the fence, or arch them back over and start training them back down another scaffold. So, if you’re looking to maximize potential for fruit-bearing wood within a given area, those techniques might add a bit (though probably more of a marginal gain there, I’m guessing).
On my current 4 tiers espalier I leave spurs on the main trunk, but i do not recall if they produced this year. If they did, it was not noticeable. Most fruit where on horizontals. Yes, it is a nice idea to form a top rail!