Hunted for years on the eastside of the crest south of I90 and seems that you could compare the tails of three bucks and they would be anywhere from full mule coloration or full blacktail or mix of both. The PCT is just kind of arbitrary, animals don't abide by human established boundaries, especially since you are dealing with sub-species which have a tendency of cross breeding.
I spent alot of time chasing Blacktails in the Alpine Lakes when I worked on the Mount Baker-Snoqulamie NF. Happy to share what intel I have. Feel free to shoot me a PM.
Clallam County has the most Boone and Crocket entries than any other county with a high buck hunt. Plus, you know it will be a true blacktail and not a bench leg buck if you hunt the Olympic Peninsula.