Vacuum Suction Not Very Effective While Separating LCD?

A few months ago i bought a LCD separator vacuum machine (after being advised that it was better than a clamp machine) , but the vacuum doesn't work very well. The LCD moves

about when i'm trying to separate the glass, is there anything i can do to improve suction???? Have already tried using the provided rubber mat and have covered the LCD in

clear packing tape to create a more smooth surface but it still moves about when i try to separate it.

Help much appreciated, I really can't use the machine at the moment. Even thought I've successfully removed the glass from the LCD its more difficult than it should be on account of me having to keep moving the LCD back in place.