This is something that can be adjusted from the service menu, to an extent. It's been referred to as the "football affect" as in severe cases your visible screen starts to look football shaped.
Here's instructions on how to adjust it. It will take some playing with these settings to get it just right.
OPERATION METHOD FOR COARSE ADJUSTMENT (first do it in NTSC Full mode)
1. Enter the service mode and select PJE category.
2. Press the 1 or 4 button on the remote commander to select the
item, and then use the joystick to change the data
3. Press button 6 to display the internal test signal (crosshatch)
4. Select GRN CENT (or any item you want to adjust). When BLU or RED is displayed, press the 3
button on the remote commander to change the adjustment color
in the order of GRN BLU RED.
5. In GRN, BLU, or RED mode, move the joystick up or down to change
the data in vertical direction, or left or right to change the data in a
6. Before returning to the service mode, press the MUTING +
ENTER buttons on the remote commander to write the data.
(You must complete step 6 to write the data. If you omit step 6 the
set data is returned to the data prior to the adjustment. Like fine adjustment, data can be copied from NTSC Full mode to other modes. And re-register FLASH FOCUS is required for it to work properly (not overwrite your changes).
Items available in PJE category for coarse adjustment
MSIZ (horizontally only)
MLIN (horizontally only)
KEY (vertically only)
For each item (and each color), there are two numbers shown on the screen, one for horizontal data and one for vertical data. Write down those numbers before making any changes, in case you want to change them back.
Ok, the things you need to adjust the football effect are pin, and key. Also you may have to work with the bow settings.
Pin is what's pushing the corners towards the center of the screem. Bow affects the over all bend of the screen, and key is a wave type adjustment.