Doing some painting has revealed that some doors fit their frames a bit
too tightly. Although many frames are not square etc, who would have
thought a few layers of paint could make so much difference? Just to
balance things out, some are too loose and have been treated to
additions to the stops.

Anyway...In one case, althought it's clear that the door is too close a
fit overall, so could use a few mm taking off one side, it also shows
that the frame has a small bulge in it, of maybe 2 - 3 mm over 150mm,
around the level of the lock. Clearly, if this was flat, it would
reduce the amount I have to take off the door and leave me with a better
fit all round.

It's not the most accessible spot, as these door frames don't have loose
stops. I've been mulling a few approaches including: A lot of sanding
(quite tricky all the way into the angle of the stop), planing (also
hard to get right into the angle) or routing (potentially a good outcome
but a bit or a pain setting up a jig for the job).

So what quick and easy approach am I overlooking, chaps?