like I said, I already tried those solutions. Moving the mouse or using the keys or clicking on the arrows near "Left, Top Horizontal, Height" have the same result. It just moves the black border from left to right or using width and height some bars appear on the screen.
For some reasons using 1280x1024 @60 or 800x600 @100 give me a centred image. The only problem is that with 1280 the screen looks like is in interlace mode. At 800 the characters are not correctly visualized. So I suppose that, if I can modify those 2 resolutions, modifying the parameters like H timing and V timing (freq, polarity, B.porch ..) to the one that my CRT understand the most, something may improve
Unfortunately, I am unable to modify those parameters from the software.