You can test for flare by measuring the film density obtained when something like a coffee can painted black on the inside, is placed in the field of view of a typical scene; high contrast or low contrast. You may indeed find for a low contrast scene, the haze on your filter has minimal effect. Whereas you may or may-not find increased 'black coffeecan' density with the filter in place during the high scene contrast test. Only testing can tell for sure.