From the posted links find the spec but be careful about assuming the capacity mentioned will be correct on your machine. Shower screen projections vary according to make so on some machines the capacity will tend to be higher than stated,
Safest way to find max is via a coin test on a tamped fresh puck. Fit with coin in place, remove and look for no impression. A 1p has been suggested. Min is before wet pucks start to be a problem.
The reason for leaving a space is to allow the grinds to expand. If limited this will compress the puck more. A bit of that may not cause problems but on the other hand it can.
