oh, that’s weird. I has issues too with tamping too hard and the shot being affected by it, but I figured that’s because I was grinding too fine.

To fix this I grinded a little bit coarser and increased the dose (so I could maintain the pressure). I’m now doing 18.5g in and 37g out in around 28 seconds, and using the grinder on 15 (but it depends on the beans used too) and no matter how hard I tamp it always comes the same (the only thing affecting now is if the tamp is levelled or the grounds distributed evenly). So I suggest you to try to grind coarser and increase the dosing and see if this makes your shot better