Looked for cracked solder joints or points of delamination/trace damage. Nothing stood out, though I can't easily see the bottom of the motherboard (removing it is rather involved). Indeed it was somewhat confusing why an area involved in vert deflection was involved with this horizontal side effect.
Did some more experiementation and found the following:
Before the unit is fully warmed up, if I press anywhere in the red area the screen output has squished in horizontal sides. If I press on the blue area, the effect reverses and the screen is normal again.
I think what's happening is the horizontal part of the beam find circuit that shrinks the display is getting turning on some how. I think that because if the screen is squished and I push the beam find button the horizontal width doesn't change. Can't be a coincidence that the squish just happens to be the same amount as what the beam find button does.
This makes it a bit more confusing because we have thermal expansion turning the horizontal component of the beam find on, and physically pressing on parts of the board turning it on and off. I don't see how a solder joint or trace issue could cause that?