Patrick, since you found out the trick would you care to tell how long they should be left out to dry? In Herme's comments to the recipe there is something about letting the macroons rest in the fridge, but nothing about it is included in the recipe itself.
I waited 30 minutes after piping before I started baking. Since I usually have a few sheets worth of cookies which I bake one at a time, the first tray would rest for 30 minutes and the last tray about 50 minutes before baking. I could not tell any difference between those that rested for 30 and those that rested for 50. Next time I make them, I might set a few aside for longer lengths of time and see what effect that has. The comment about letting the macaroons rest in the fridge overnight -- I had assumed that that referred to the finished cookies rather than the piped batter, but maybe I was wrong.
The cookies look great. Flat and uniform and good toasty color on the hazelnuts.