in my opinion, using "granular" to mean "fine-grained" is a mis-use of the word.
granularity as an attribute does not behave like many/most attributes where the relationship between the abstract attribute and the comparative/superlative use of the same term as an adjective is semantically clear. consider a property like density. if you say an object is more dense, the meaning is clear. likewise for many similar attributes: transparency, reflectivity, ductility, etc.
granular means "consisting of small grains or particles". among antonyms for granular merriam's dictionary lists: dusty, fine, superfine, ultrafine.
therefore, it seems incorrect to use granular to mean fine-grained and even more obviously illogical to use the comparative adjective form, e.g. "more granular" to mean "more fine-grained". if something becomes more "fine-grained", this typically means moving towards a condition of being not granular. therefore, it actually makes more sense (though is still not really semantically valid) for "more granular" to mean "more coarse-grained" instead.
my recommendation would be as follows: if you really want to say "more fine-grained", say exactly that instead of "more granular". in the (rare) case where you really want to say something is more grainy - irrespective of the size of granules - then go ahead and say "more granular", but be prepared to be misunderstood.