Thanks for that very useful link. I've been looking for a comprehensive guide like that for some time now.
I see your point about the soffits, but I think I'm SOL there. The soffits that feed that portion of the roof are indoors. Seriously, whoever built those two rooms didn't care that much about thinking things through.
These two pictures are looking towards the master bedroom (the one with the issue) from the sun room, which is where the roof ended and the soffits are located.
Since we are never in the sun room, it gets really hot. If the soffits get any air sucked in, it will be hot.
But you got me thinking... maybe my solution is to try to cool the sun room so that it will provide the chambers in the roof with cooler air through the soffits. Maybe I just need to keep it at around 80 or so degrees. Not exactly arctic temperatures, but cooler than whatever it has in those chambers...