Based on the comments before me, I modified today's example to be:
- 40 ml gin (Beefeater)
- 20 ml elderflower liqueur
- 20 ml Amaro Nonino
and I think this is the direction in which to continue.
The next iteration would be:
- 45 ml gin
- 15 ml elderflower liqueur
- 20 ml Amaro Nonino

Also, given the total volume, a Nick&Nora glass would work well.

Far, far too sweet for me. I created two cocktails with the same Amaro Nonino, and St-Germain, and doubled the gin, and split it between two cocktails.

Delicious cocktail, although I find it is a bit farfetched to see it as "Paper Plane" variant. IMHO it needs a bit balancing as it is on the sweet side.