I mix acid before coating. I did not added to the gelatin before. I do not know how it behaves, but that sounds quite reasonable. (albumen binder contains acid too)

I think 1 part %5 citric acid 1 part silver nitrate mixed before coating would work fine. I prefer %10 citric acid, but I fear 1+1 is unnecessarily diluted, so I have decided to mix %20 citric acid and add half the amount (2 + 1 ). I might even increase it to %40 to lower the dilution of SN. I am doing some testing with salts at the moment myself.