The component parts have the potential of resulting in a characterful drink. Recipe as written is way too Montenegro heavy for me. I went 2:1 tequila to amaro second time and it wasn't quite right, even after doubling the agave and adding 2 drops of saline. I want to make this work...
We suspect that the problem may not be the volume of the Amaro but the particular Amaro chosen, Montenegro, which for us is a workhorse and not a racehorse (at 45ml, a racehorse is what we think might be required here). We might try Nardini, Braulio and Nonino Quintessentia to cover a few bases...maybe even Averna. We salute your perseverance.