I wonder what the granularity is? Can I move to a WA area with middling CoL and benefit from that Seattle-derived salary bump? If they take issue you could make the claim that you would normally commute to Seattle so you deserve the Seattle remote rate.
You can even rent a trailer in the Seattle area and hire lawyers to explain you how to game these rules in the most legal way. When 500k/year are at stake, employees will be very creative (and, afaik, they are hired precisely for their creativity and outstanding intelligence).