Well...

My experience is that before the big change, I had been farming Silvanus for a whole lot of fights, with 2 girls left to drop... I heard that the recent fights without girl dropping would spread out among the world bosses, so I got exited because I also have a farm-able girl waiting on Ninja Village and one on Grunt...

And then the change came...

I kept farming on Silvanus (unless to get the event girl). Now silvanus is capped at level 170, I got the Val Abrael (already had Val Red Battler), then kept farming silvanus. Never let the combativity reach 20, always fighting silvanus. Farmed him so much I think he is dry in the bones. Still no girls dropping...

I almost feel like farming another... Maybe it will "unclog" him... But the developers said that the bosses now work independently with their own drop rates... So I keep fighting the skull-man... Hoping to see Leeditt or Queen Titania someday...