Starting to understand what Ford did there (thanks). By having the spring coil a little tighter at the top they were able to eliminate the extra metal seat and have it rest on the support. The M-18000-ZX3B dampers also came with the support you have pictured, I'll compare them to my stock ones to see if they are the same.
I am having a had time telling. Did your springs also reduce down to a 4" at the bottoms as well? It looks like the M-18000-ZX3B struts themselves have a 6" seat. I'm a little surprised that the coil doesn't try to move around.
Hopefully later today I can pop the front tire off and take a closer look on how the stock suspension is set-up.