@hangint3n - Just try it without the portafilter and you'll see that there's a gentle flow of water from the boiler. It's just not enough to saturate the puck. That's where turning on the pump for a few seconds gives pre-wetting enough of a head-start to be able to fully saturate it.

The preinfusion / half way lever is inconsistent. It all depends on where the thermosyphon is when you pull it, and there is no way to know where it is.

For me i found to "preinfuse" or "wet" the puck i just do a full lever pull for 2-4 seconds, pressure does not really ramp up to full 9 during that time so depends on the coffee and what variables it has on when its dialed i just do 2sec pull, then half way until 15seconds and close and i pull the shot.

This is the only way i found to preinfuse with consistent results on the e61.

Or use a flow control kit.