I read a while back that Pretter had used the anhedral stab on the Curare because he had theorized that the stab was being blocked during stall turns, making recovery take longer. So yes, I think it was originally about trying to make sure that at least some of the stab was in the airflow all the time. I'm sure a secondary benefit was changing the pitch coupling behavior in knife edge flight. An anhedral stab essentially acts like a down elevator mix in that situation.