Since you manage to get the ratio and timing you want (without channeling?) but end up with sour coffee I doubt the issue is the grinder. I suggest you try the following:

1. Longer warm up.
2. Higher boiler temperature.
3. Darker beans.

So the 270 adjustment ring definitely helped, but sadly nothing that I am really happy with.

I guess I am going to sell my Bezzera Unica then. I think there is a buy/sell board here as well?

I saw that you complained that your shots were too sour. I find that almost all third wave roaster produce roasts (even for espresso) that are too sour. The only exception in Edmonton is Ace roaster. Even there, I find the roasts to be inconsistent. So these days, I am trying different Italian coffees that I can find at the Italian centre shop. None of the Italian coffees that I've tried are sour.

Masao