[old_tv_nut]

Geometry is probably within spec. As to the picture being brighter in the center: hook up a DVD payer (which will run at the standard 59.94 fields per second instead of 60.0 of some test gear and sources). If the bright area slowly moves vertically, it indicates some kind of 60 Hz hum is present - probably a bad cap somewhere in a power supply section.
If the bright area remains in the middle, you can chalk it up to a design limitation, or look for some way that the vertical sweep may be producing hum in the video section power supply.