Isomnia sometimes leads to productivity.
I "see" now, why I had a problem installing my Garrett CAC that was specifically designed for the F-150. I took the risk so you don't have to, and am now updating the thread for clarity.
It does indeed appear the lower grille shutter assembly is different (at least on the 2018 Expedition, didn't bother to check against prior m.y. expys cuz, I have '18, lol). According to Garrett's instructions, if you "peel away/unsnap and remove" the following piece (highlighted in green) with a pick tool, it provides the necessary clearance to mount the new CAC. A side benefit of this is of course the grille shutter module is still attached to the main housing. This is true if you have grille shutter assembly JL3Z8475B.
My grille shutter assembly on the 2018 Expedition is JL13Z8475B.
It is just a weeee bit different, as I mentioned before, it doesn't have an additional removable frame.
Pics/diagrams...
F-150 "3Z"...
https://i.ebayimg.com/images/g/dLYAAOSw-sZa1ioz/s-l400.png
Expedition "1Z"...
https://dz310nzuyimx0.cloudfront.ne...dfc46588/93f4a39d262a5bf2ac75131ccf3904a9.png
As I said before I don't regret, taking the plunge, buying something that was not proven to fit on an Expedition, but I'd thought I'd provide further explanation for anyone who may be "on the fence". This additional information hopefully will provide confidence to go forth either to move on to something else, or take the plunge.
I would caution, that if all Expedition's or at least all 3.5 Ecoboost equipped Expedition's use the exact same shutter assembly as mine, the probability of using a different aftermarket CAC will likely present the exact same challenge, as is present with the Garrett.
I knew the upper shutter assembly was different between F-150 and Expedition, but now I have my confirmation for the lower too.
One glaring difference in the upper assembly, there are two air duct openings at the top of the housing assembly that helps feed cold fresh air diverted from the shutters being closed, up to the front portion of the hood, that channels additional air to the factory airbox.
Expedition owners get screwed, LOL. The upper portion of the grille assembly for Expedition does not have these two openings.