Can a SceneKit Physics Field affect some nodes but not others?

I have attached a scenekit physics field to a node:
let dragField = SCNPhysicsField
dragField() ballNode.physicsField = dragField

let dragFieldCategory = 2
dragField.categoryBitMask = dragFieldCategory

The halfExtent property of the dragField is set to slow down other nodes passing only through the ballNode. This works fine. However, I have two nodes moving in the scene (NodeA and NodeB) but I only want NodeA to be affected by the dragField. I am not sure how to set the categoryBitMasks to make this happen. In SpriteKit there is a property fieldBitMask which is attached to the physicsBody of the Node which you want affected. i.e. NodeA.physicsBody?.fieldBitMask = dragFieldCategory. There is no such property in Scenekit so how can I have the physics field selectively affect some nodes and not others.

Any help would be appreciated.