Interesting trick with the canvas. Never tried it. I am not quite sure I understand how you do it Gene. Would love to see a video.
One correction though. You need the wet passes (and dry passes) to be in the direction of the nap. Usually (not always, you'd need to check as upholsterers do make mistakes or at times it may be on purpose) a velvet sofa will be cascading.
That means that the nap direction will be going from the top down (like a cascade) which means that most cushions when placed correctly, the nap will be away from the zipper. Most, not all.
Afterwards you brush 90 degrees to the left, let it dry a little (you may hum a song of your choice), 90 degrees to the right, let it dry a little, and supposedly last brush in the direction of the nap. Woof.
I've also done the last one against the nap and at times it looked better, though you have to test.