Java: Datapack value variable selector

21w39a added advancements that make use of world depth and height properties, these values are hardcoded. The caves and cliffs fall from world height has the conditions world bottom, world top and fall distance set to -59.0, 319.0 and 379.0.
Why is hardcoding this a problem? This is a problem because this advancement will now not work in a world with smaller world height. My suggestion is being able to assign a json object value to the value of another object. In case of needing the y coord of the bottom of the world you could set the value to dimension.generator.settings.min_y which would look like this in json

"position": {
  "y": {
    "max": dimension.generator.settings.min_y + 4
  }
}