Your own words dont make sense.
“Pick a zone to start with that you know can be HQ”
If youre starting, then all four can be HQ.
This is exactly how it works.
Let's say you've never opened a box before, the bonus could be any of the 4 zones.
You open NE, it's not there. Now it could be SE, NW, or NW, but it can't be NE (you just opened it, and it's not there).
Next, you open SE and get the bonus, yay!
Now, it can be any of the 4.
There are countless reports of people getting the bonus in the same chest back-to-back.
He doesn't mean "all 4 can be HQ" as in, they are all HQ. He means "any of the 4 could be HQ". Once you open one (and it fails to be HQ), then that's no longer true. Only 3 of them could be HQ (the three you haven't tried yet).