I wrote up a Google sheet to help with combat balance.
Input your party stats and the sheet can generate suggested enemies, or evaluate encounter difficulty.
The methodology I used is based on average damage per round. And while there are many factors accounted for, there are some big ones missing like radiation resistance. I have only tested this thinking on about 10 combat encounters, and the results have been good for me so far, but this is admittedly still pretty rough. Hopefully it’s better than just comparing HP. I apologize in advance if this sheet leads anyone into an unenjoyable encounter or TPK.