wilburpan I’m sure that the increase is not due to retention.
I understand what you are doing. But you didn’t follow my suggestion of not zeroing out the scale first when measuring the weight of ground coffee.
Make a note of the weight of the container where your ground coffee ends up. Grind into it as you usually do. Put that on the scale. Subtract the weight from the container. Does that still read over the 18g you put in?
I’m trying to assert your scale is not the problem by not zeroing it out first.