Actually it somewhat works but you need to set some sensible values for refractionTexture.lodGenerationScale and refractionTexture.lodGenerationOffset (which are both 0 by default):
1 and -4 are the default values used by the glTF transmission helper.
The formula is: final LOD=LOD_computed_from_roughness*scale+offset.
Of course, as it is using LOD to fake bluriness it may appear blocky and is not very precise, but it works as a crude approximation.