Seed for an additional dimension doesn't appear to be used

I export the worldgen settings for multiple worlds with different biomes at 0, ~, 0.

I merge the worldgen settings into one json file and use that to create a world with multiple overworld dimensions.

When I switch between the dimensions using the /execute ... tp ... command, the dimensions are all identical. They all appear to be created using the main seed outside of the dimensions structure rather than the override seeds specified under each dimension.