I had trouble with Stockfleth's until I realized if I didn't take the online and video demonstrations too literally, I might make it work and it's now working well. The point, I think, is to distribute the grounds fairly evenly through the portafilter and in doing so pre-fill any air gaps. Tamping finishes it off. Unless you're a professional barista needing to work fast, the Stockfleth's pre-compression doesn't even have to happen in one move.
I found at first that I was getting donut extractions (viewing the bottomless portafilter) where the coffee was too dense in the middle of the portafilter and would start dripping in a ring around that. So instead of doing a fairly level press over the top of the coffee cake, I create a parabolic indentation at the middle to leave more coffee at the edges and correct the tendency for too much density at the middle. I then do a nutating tamp (gently rolling the tamper like a coin rolling on its edges).
Also, my corrupted version of Stockfleth's involves making sure there's enough coffee in the basket that the heel of my hand can easily press it down. If the part of my palm near the thumb doesn't quite reach to compress the coffee with a clockwise turn (portafilter handle held in left hand and right hand presses into the coffee) I'll turn the portafilter counterclockwise and compress with the outer edge of my palm. With a lower dose I might switch from the double basket to a single one so I can still press the heel of my palm into the coffee cake from the top of the basket.
I hope that didn't seem too complicated.
