Here is what I made...nothing fancy...just cobbled together in a few minutes...3x5" (ish) piece of 18 GA metal with a 1/4 x 3/4" slot cut in the middle. 1/4" steel rod for a handle, inserted into the slot at a steep angle and welded in place...I wish I had made the handle longer though...like 36" instead of 28".
The steep angle of the blade allows you to turn it on its side to get between the HX tubes, and also behind...can scrape the backside of the tubes and HX ceiling too...just flip the blade over once its behind the tubes, the angle allows you to get right up to the ceiling and down to the back wall (including the back wall...but that is a little cumbersome...would be better with that longer handle I mentioned)
The other things I've tried was my Sooteater brush...works ok, but kinda messy and hard to control precisely...barely fits between the tubes also.
You can also wipe down the upper parts of the tubes with a Scotchbrite pad if you don't mind sticking your arm clear in there...like I said, can only get part of it though...and you have to be part contortionist.
I really hardly use the scraper that comes with the VF at all since I made my own.
Here's some poor pics.
View attachment 272461 laying on its back
View attachment 272462 laying on its side
View attachment 272464 laying on its face