Ex raid gyms eligibility tweak?

There are 3 gyms in my nearby city that I usually raid in, hoping to get an EX pass. I have seen them spawning Mewtwo on the scanner (at that time they weren't down). I still had no EX passes. I raided them pretty much every week after the Eon duo were released, and that is the weird point, every week indicates no Mewtwo spawns. The 3 gyms were all eligible in the same cell.

The only thing that I can come up is that the centers of the respective level 18 cells are not in the OSM park area.

Why level 18? All of their level 17 and level 19 cell centers are in the area of parks.

That should explain why there are fewer EX passes.