Mesa biomes not modifiable by addons

Hello, I have been working on an add-on lately which involves modifying the vanilla biomes. I have had success with most biomes, however, whenever I load any of the mesa biomes, there is no change. I thought it might have something to do with the "mesa" tag in the biomes' definition files, but when I replaced it with the custom tag, "mesa_modded", there was still no change in the biome when loaded. What is supposed to happen is that the mid, floor, foundation, and top materials are to be air. This works with all non-mesa biomes (that I am aware of). Attached are the mesa biomes' json files, as well as another biome that is working with these changes. Also attached is the full add-on. (I set this issue to private to prevent others from stealing my add-on)

 

Below are some screenshots showing the issue:

(Note that there are features modifying other parts of the biomes)

Not working:

Working: