The 3K NAM has a tongue of H7 fronto well ahead and north of the main low. It's solution alone doesn't seem outrageous. South of that, you are at the mercy of WAA and hence the more constricted QPF field.
Is it right, not sure. But we had something like this in early Jan 2022. There was a narrow but intense band of S+ shown by the HRRR over BOS and just south. It dropped like 4" near BOS before the main stuff even came in. It was pounding here with nothing 5 miles to my south.