I dunno, I think the cut-off is going to be pretty sharp wherever it happens. Location of the gradient can easily change, but with that stout high to the north and a lot of cold/dry surface air lodged in the lowest few thousand feet, I think synoptically it makes sense that it cuts off pretty quickly on the north side. I've got plenty of experience, lol. You get those half evaporated small dry flakes that see their arms shrunk in the lowest few thousand feet while it's ripping good flakes up at 4,000ft+. That's a pretty stout surface high.
Mid-level lift will be constantly fighting on the northern side with dry air trying to bleed in from the north. Best guess is there's a strong band somewhere near the northern gradient and then north of that band totals just plummet. Where that is TBD.