Paterson have soft base for papers, like spoonge (atleast my printer has it). Theory is that this paper base will adopt (bend) itself (an paper on it) to any shape needed to have firm pressure of negatives on paper. So, in theory it will adopt paper in such way that it will eliminate that space (part of millimetre) between negative and paper which is made because of negative guides, and thus negative is flat pressed firmly on paper.

In my case Paterson printer works for me, but you really must try it to see will it work for you.

Paterson also have printer without negative guides, with same soft paper base, so maybe that will work. It is made for 24x30cm paper not 20x25, but nobody stops you to use 20x25 paper in that printer With it you must place negative directly on paper, not insert negative into guides. And this bigger printer have thicker glass than 20x25 printer (I even think 20x25 printer have plastic and not "real" glass while bigger printer have "real" glass, but can't tell for sure).