The only time I've ever gotten drops during boss battles is when the judge matched my character type, Charm to be exact. Also, I've noticed that the judge I need seems to appear less often than the other two, Hardcore and Know-How. Say what you want, but for the first two days of the current Halloween event, I got no drops and the only judges I had were Hardcore and Know-How. Maybe the Charm judge actually activated while I was asleep, but the third day the Charm judge activated for me and I got the first girl from Gruntt in several tries, then switched to Dark Lord and got his girl in just 2 tries. This seems to work for event girls fairly quickly, but still takes a super long time now for regular boss girls. The last boss girl I got to drop, Sylvia, took about the same length of time, over 2 weeks. The one before that, The housemaid, took over 3 weeks.

I'd suggest only trying for girl drops when the judge is active that matches your affinity. Otherwise, just farm the boss that has the highest money drop until your judge activates. You're probably wasting time doing it any other way.