A bigger crayfish than papershell yet does little digging into pond banks is the Northern or Virle crayfish (Orconectes virilis aka lake crayfish) present and is the most common and widely distributed crayfish in IL. It is one of the biggest crayfish in Kansas. TJ had O.virile crayfish in one of his ponds and they became too abundant, to big for good fish predation and denuded the pond. Contact him for some of his experiences with northern crayfish.
IMO if the papershell are not maintaining a breeding population in your larger pond then the habitat is not conducive to PSC crayfish, similar to maintaining FHM in a pond. FHM can be maintain a breeding population in a pond if the habitat is correct.
If it were my situation. I would move a few papershell from your main pond when ever you catch them in traps into your new forage pond. Your forage species will tolerate the PSC and PSC will keep algae and plants minimized or barren in the forage pond. Then move abundant individuals from the forage pond back to the main pond.
http://naturenorth.com/fall/crayfish/Fcray2.htmlhttps://nature.mdc.mo.gov/discover-nature/field-guide/northern-crayfish-virile-crayfish
