I have found in my coatings that 15% gelatin in water results in the dry thickness of about 15% of the wet thickness after drying . This is very approximate but should give you a general idea what happens in drying...

I have used 300 um (12 mil) gap when I have coated my film coatings but it certainly IS a bit thick, and can take 5 minutes to clear in fixer.

I think I've always been too high in gelatin compared to silver, because of dilution in washing and addition of gelatin afterwards. Maybe a bit too high coating temperature, too, leading to need for more gelatin.