Im not familiar wih Imat but id say the rubber thing is part of a Crema enhancment system. If it comes out easily you could try pulling a shot and see what happens.
How long does it take to pour a 30mil for a single shot? You should be aiming at 20 - 30 secs.
Have you tried adjusting your level of grind?
Also the freshness of your coffee can play a big part in the amount crema produced.