@roleypup thanks for the detailed report! Even though you “drank by feel,” sounds like you got it right.
I make my own carb / electrolyte drink mix that has about 300 mg of sodium per 1L bottle. That seems to work fine for me for rides under 3 or 4 hours. Longer than that and I find I need to increase my sodium intake, and substitute the Nuun tab for a Precision Hydration 1000 or 1500 sachet. A bag of potato chips (ie “crisps”) also helps!
Again, awesome job! Audax’s are really starting to interest me so all of this info is super helpful.