Considering the different sizes of the targets, I'm not sure what all this means. Like, while there are hundreds of denominations of christianity (though that seriously overrepresented Catholicism), atheism is barely more specific than 'Other' in terms of moral foundations and systems.

As long as you're comparing groups with different degrees of dispersion, it is going to be trickier for one side than the other. The more degrees of definition, the more opportunities to miss one as an outsider and slip up.