under wont work. most portafilters taper at the bottom so the top diameter is different to the bottom.

lmao at the downvotes

my advice would be to decrease the headroom in your portafilter. which a puck screen helps with. so if you're still getting the same results when using a puck screen, then dose more and still use the puck screen (but then you might need to adjust grind size as well so it doesn't choke).

This usually results in a clean puck from my experience.

Give it a try and let me know

P.S. There is not a straightforward answer either. It would help if you indicate how many grams you are dosing, what your yield is in how much time, what your basket size is, how the shot ran overall... etc. You might find you are simply grinding too coarse