I’ve been using my Rancilio Silvia with my Eureka Mignon Manuale grinder to pull two double shots daily for about a year now. I’ve been working really hard to maintain consistency with my distribution and tamping, but the one thing that has been consistent is how uneven the extraction is.

Nearly without fail when the coffee first emerges from the bottom of my bottomless portafilter, it emerges from back to front, and blondes much faster at the back then at the front. I know this is causing uneven extraction and unnecessary bitterness. What could be causing this, and how can I improve? Is it something intrinsic to the machine or am I habitually tamping crookedly? How can I diagnose?