Wayne Collins, this cocktail's creator, originally used equal parts as is usual for a classic Negroni, and after trying various other formulations, I've...
Made it side by side one with Lillet Blanc and one with Cocchi Americano- the latter is definitively the right choice! Incorporates the Suze better and has overall a more negroni-feel. Lillet Blanc in contrast doesn't produce a rounded palate