Question About The Dominant Force Ingredient

Hey, I have recently been grinding around Twain Lake, originally gathering ghostly essences for the boss altar nearby, until I stumbled across a possessed armour stand. The first one I killed dropped a dominant force, which seemed like a pretty decent thing to grind for. I began to look out for them a bit more, and dropped two more dominant forces on the next two consecutive kills. Since then I have revisited the area to grind more, and I must have killed tens more of the things, but not a single one has dropped another dominant force. Is there a reason for this, like a cap or something? or did I just get really lucky the first three kills?

 

From my peraonal experience with grinding it you were lucky with your first ones