Why 53mm baskets?
Really interesting article in the 3rd edition of the La San Marco Coffee Break on the advantages of a 53mm group head over 58mm. It’s all to do with the well known “Darcys Law” which is to do with liquids passing through porous compounds . Basically better to go deep and narrow, than wide and shallow.
Having a deeper path for the brew water to move through, extracts a better quality espresso , than a shallower path. Particularly when the pre-infusion is applied, the ‘puck” and provides a more resistant channel, and further improving extraction.