Wayne Collins, this drink's creator, originally used equal parts as is usual for a classic Negroni and after trying various other formulations, I've found...
I agree with a number of others here - reducing the Suze a tad makes the drink more balanced. So the ration became 1 gin/ 1 Cocchi Americano/ .75 Suze. I had no grapefruit twist but a dash of grapefruit bitters spread over 4 cocktails worked well.