The spice mix is added at 2.2% of the brine weight. It's not related to the meat weight from that point of view.
1000gm of brine (approx 1 litre) would have 22gm of the herb/spice mix added. Of this mix, as an example, 4.4318 % is juniper berries, that's 0.974gm (about 1gm) - 8 or 9 juniper berries - I weighed them to check! Boiled in the brine, I'd say that's plenty enough given that it's injected.
FWIW, I used 5 berries in 500ml in this one that I made using my recipe, for Christmas:
HTH
Phil