Why is lightmap resolution different across certain objects?

The problem:

Environment geo shows different/incorrect lightmap resolution, even though the lightmaps are generated at import, and all objects have scale at 1 and lightmap scale at 1.

Expected behavior:

All environment objects should show a unified resolution (with some small degree of error.)

The geometry is imported with only one UV channel. The lightmap UV channel is generated at import. Diffuse UV is painstakingly mapped so that all texel resolution is uniform. The objects themselves are never scaled.

I set the importer to Generate Lightmap UVs = true. I set Resolution in the lightmapping window to a specific value (in this case, I've set it to 2 so I can demonstrate the discrepancies with the lightmap resolution render overlay.) I see that some objects have a lightmap resolution seemingly 2/3x, even 1/2x (give or take some error) the expected resolution.

EDIT: For the life of me, I can't include an image-- process gets stuck at the resize portion where the buttons to accept or cancel remain unclickable.