Choose the closest match by flavor goal: bitter backbone (amaro + orange bitters) vs lighter orange (Aperol + orange bitters).
Use the table ratio to replace Amer Picon (then taste after dilution-free sampling).
If it tastes too sweet, add dashes of orange bitters (or a bitter liqueur) rather than more citrus syrup.
If it tastes too harsh, dilute slightly with a splash of water or chilled spirit base (and re-taste).
For stirred cocktails, let the first mix sit 30–60 seconds so the bitter and orange notes integrate.