I haven't read the regulations in detail, but my broad knowledge says no, it would not be legal. My basis for this comes from something mentioned in Kyle's video on the Mercedes W13 upgrade with the slim sidepods and the mirror mount wings.
I'm recalling this from memory, so the terms I use may not directly correlate to the wording in the regulations.
In the video, he explains that along a longitudinal vertical plane there can be a maximum of two distinct intersections. On typical sidepods with a standard undercut, you would get two intersections; one from the top surface, and one from the undercut (screenshot I quickly took of the video):
Whereas on the Merc, you get one intersection from the mirror mount wing cross-section, and another from the sidepods:
This is why the Mercedes sidepods have no undercut, because (to my understanding) if you had the mirror mount wings and an undercut sidepod (like previous years) there would be three intersections.
If you had the "wing" shaped tunnel like the shape in black, then you would have three intersections at the overhang; one at the top of the "wing", one at the bottom of the "wing", and one at the top of the "normal" sidepod shape, not including any undercut. The only thing that may allow it is how high that reference plane goes (which I don't know). Obviously it's these kind of weird, fine margins that can win you championships, and it takes someone more patient than I to read the technical regs to their fullest extent.
"You can't argue with stupid people, they will drag you down to their level and beat you with experience"
- Mark Twain