Using sprite atlas late binding with non variants

I am trying to set up sprite atlas late binding so that I can have lower res sprites for lower resolutions.

I can get this working when I use an atlas variant to create the lower res atlas but I am finding that the sprite quality isn’t as good as I would like.

I would like to be able to supply my own lower res sprites which I then bundle into an atlas but I’m finding that this isn’t working. When I pass the lower res atlas to the late binding callback the sprite isn’t visible (a SpriteRenderer in a scene).

I believe this should be possible as I have seen it mentioned in the docs that you can use late binding to supply localised atlases, not just lower res ones.

I have made sure to give the lower res sprites the same names as the higher res ones. I have tested using GetSprite(name) on the lower res atlas and this returns a sprite as expected.

Is there something that I’m missing? Any help would be appreciated.