Question about the new attributes and fog

Hi, I was playing around with the new attributes that are added to the snapshots and I can't seem to get the following to work:
I want to make a biome with a custom fog distance so that I can set the mood for an adventure map I'm making. I have been trying to figure out how it works but clearly I'm not up for it. I have used a template for a plains biome from a datapack generator and I can /fillbiome the new biome in no problem. Unfortunately once I add this:
  "attributes": {
    "minecraft:visual/fog_start_distance": {0.0,
    "minecraft:visual/fog_end_distance": 16.0,
  },

to the top of the json, relogging into the world tells me that there's an error in the selected data pack.
Alternatively I tried the following too (not that I'd know if either is correct)
  "attributes": {
    "minecraft:visual/fog_start_distance": {
        "modifier": "override",
        "argument": 0.0
    },
    "minecraft:visual/fog_end_distance": {
        "modifier": "override",
        "argument": 16.0
    },
  },

Any guidance on what I'm doing wrong?