Fortunate enough to have some Amer Picon, I tried this again. Intrigued by the origin story, I sought out the GumboPage.com site referenced by Difford's under History. Difford's indicates the each ingredient has been reduced by one third, but I believe in fact only the amount of gin has been altered. I wanted to try the original recipe calling for 2oz of gin but as I only had Plymouth Gin Navy Strength, I reduced it as per Difford's adaptation thinking it might approximate the original. Very tasty but 1) as per comment below, maybe some acid would elevate this drink, and 2) I won't be driving tonight!
I've never had Amer Picon or Picon Amer or whatever it is. Today I bought a bottle of 'American Picon' by the New Liberty Distillery in Philly. Used that and The Botanist and Luxardo Triplum (my fave) and the end result was particularly, bitingly bitterly amazing... I've been testing a variety recipes today after stocking up on some things. And this was the mic drop I needed.
Although a fan of Amer Picon in cocktails, I found this one a bit 'flat' at first. Added a knife's tip of citric acid dissolved in 2 tablespoons of water and 2 drops of 4:1 saline solution and that made a good cocktail a great cocktail (to my taste).
Thinking about your comment as I drink this, although I really am enjoying it, you are absolutely correct; it could benefit from a bit of acid. I have citric acid powder which I use for cooking, I was curious if you have other ideas as to how to introduce some acidity.