Despite using the WDT extensively I never had good results with a bottomless Portafilter. My machine is an old Saeco Classico but it still works. But I always suspected the water flow on it wasn't good. The center of the puck is always depressed more than the rest. Adding a Portafilter screen and paper filter seems to have fixed the problem. Shots now don't squirt but come through center of the Portafilter. I suspect high end machines don't have this problem but the Screen really fixed the problem for me.