3D alignment error question

Is 3D alignment error equation (11) from the SI of the original cryoSPARC publication such that it is an absolute measure that can be compared between datasets (or at least between subsets of the same data)?

Unrelated question for @apunjani, was there a reason to shift the images to the map via S_l(t) instead of multiplying the projection by S_l*(t)? Just a better implementation?