Fluxgrip Holding Force Variation

We are seeing an interesting behaviour with our test gripper. When an armature plate is offered up to the fluxgrip, and it is switched on, we see a very powerful holding force. However, when we switch on the fluxgrip without an armature plate touching the magnetised surface of the gripper, the holding force is much much weaker.

Is this behaviour expected, and is there a way to overcome this?

Thanks

Thanks Pavel