Yes, I used that video. The issue is that the areas cut out of the slate for the pockets are quite a bit deeper than the example Diamond, plus they have a significant chamfer on the edge. That, along with two thicknesses of 3/4" plywood under the slate means that the cloth needs to be pulled a lot more to fit against the inside of the pocket. I ended up needing to cut farther up toward the table surface than I wanted, which required a skirt to cover the slits. I'm still not fully satisfied, but have moved on to getting the rails complete before I decide if it's worth trying something else to fix it fully.
BTW, I do really like your videos, I just wish they were less Valley focused, since most furniture tables use staples instead of glue to hold the cloth in place. Also, in regards to that one, when you have the user back off 3/4" from the full 2 1/4" stretch, wouldn't it make more sense to have them back off by 1/3 the total, so you could use it better on large and small tables? I'd expect if someone wanted to put 860HR on a 12' snooker table for some reason, they would end up with a stretch calculation that would be off...