Don't try and figure it out . . . just use Taco's Tool:
http://www.eq2interface.com/download...fo.php?id=3395
If you use my Mapper2.pl, it creates crosshairs and gives you the locs for the first 2 cords and you use an image program to pull the Bitmap x/y cords off your finished image.
Mapper2:
http://www.eq2interface.com/download...fo.php?id=3936
I almost never have to readjust my zonerect after I use Taco's tool combined with my mapper output.