The way i approach those is based on the way i position my thumb. I tend to have mine all the way on the bottoms, but for big stretches I lower it.
I think the size of your hand will influence your natural way of holding it. If you have smaller hands that would make it difficult.
I also move my hand sometimes. It doesnt stay on one position.
So i combine thumb more on the low of the neck, and moving my hand.