While dialing in a bag of new beans, i changed depth on tamping. Always read "be consistent", but was never told to find the right pressure. I guess that makes sense, but what difference a millimeter further into the basket makes. There was always something missing, then I pushed just a hair deeper and now I'm getting fuller body. I use level tamper so it's easy to keep that setting.

There's a range that is hard to keep consistent, below where the bed "firms up" and doesn't seem to compress any more. Without a scale or force-indicating tamper, that point where the bed seems to stop compressing and starts to push back, or slightly firmer, is generally a reasonable place. It isn't so much "x mm", but a feel. The depth will vary a bit by roast level, origin, processing, and grind setting (with mass of the dose held the same).

I guess that would indicate manual tamping with enough experience to feel that point.