OK, I revisited this again and I figured out why I left empty handed . You prob. only want to read this if have OCD or are just AR about systainer stacks.
Seth is correct, CT-SYS is a combo of a SYS 1 + a SYS 2. The problem is, in systainer world 1+1 does not equal 2 and 1+2 does not equal 3. [huh]
Seems a SYS 2 is a bit of an anomaly being 1.5x the height of a SYS 1, not 2x. A sys1 stacked on a sys1 is the same height as a sys3 and a sys1 stacked on a sys2 is taller than a sys3 ! So for me the problem was/is that the CT-SYS does not play well with the heights of a SYS4 - which is my typical stack height for travel. I was playing around and couldn't get a ct-sys and a stacked sys1 to equal the same height of my various sys4 combos. And now I've had the epiphany - that darn sys2 is the step child, and hence the ct-sys.
If you want a ct-sys to be the same height as typical combos of systainers you likely carry to a jobsite then you are going to have to ditch the top sys1 of the vac and replace it with a modified sys2 so that the resulting combo is the same height as a sys4. Keep in mind the new SYS-Combi II poses the same height issue.
Perhaps many of you realized this already, but I haven't carried anything to site in a SYS2, so it's the first time in 15-20 years that I've experienced this. Bottom line to me seems that SYS 2s need to be carried in pairs. [unsure] You may not even care about the various stack heights, but I like my stacks to be flat across the top creating a shelf if you will.