5/8 is the distance from the feedpoint down one leg, across the hoop and back up to the tip of the antenna, that would be a more likely source of the new measurement than my other idea including a 1/2wave mast,
i don't think a 5/8 wave tall version would give a good match to coax or perform well.
I use to make a similar claim that the A/P was a 5/8 wave. I've changed my mind though and now believe it is a very effective vertical 1/2 wave.
I made the taller model to see if I could scale it to 22' feet, and see how it worked. I ended up with it near 14' instead of the stock 11' feet. The 22' foot idea did pretty much as you suggested and I was no able to get it to match. I stopped fiddling with it, because I did not get an answer to my email to Tagra. Some folks just don't like questions!
My comment about brexit was in jest. Corruption is ubiquitous in our World.
Do you hear any local comments about the BT-101?