Hi, Deni,
If the stated resolution of the monitor is 1920 x 1024, then your pixel ratio is 1920/1024 or 1.88 to 1. I believe that at that ratio, you'll be mapping height and width proportionally. The closer you can come to that ratio in setting your display, the closer you should come to a proportional comic page.
Like builderboy said, check to make certain that you have the latest drivers for both your monitor and your video card. I would be sure that you've selected your new monitor as the default. The 1280 x 1024 makes me suspect that your computer might still be looking at the aspect ratio of the CRT. Try on-line support for the manufacturer of the monitor. Often times you can get "chat support" with someone who can solve your problem immediately.
Good luck.
The scans you see on DCM are done by hundreds of different people, and the variety is built into the source - i.e. there are NO requirements for the scanners or the scans. Tastes and techniques vary widely. Be happy we have as much as we do. And "Variety is the Spice of Life.
Peace, Jim (|:{>