Judging from the BAT and the screenshot, and the fact that you're running monitors at different resolutions, I'm going to hazard that you're running in dual view rather than horizontal span. Your BAT, however, is configured for horizontal span.

When using the --margin command command with maximizer, the four numbers are used much the same way as margins in MS Word or the like, defining the amount of space between the edge of the screen and the edge of the space used by WoW. So, for instance, when you define the left-monitor instance of WoW with a right margin of 1680 while running in dual view, you're telling Maximer that you want a margin of the entire width of the monitor and you get an oddly compressed window like what you have.

I'm not at home to double-check this but there should a flag like --device:x or something of the sort that defines what monitor to display WoW on when using dual view.

Of course, if you are using horizontal span anyways then this post is clearly hogwash and you have some other sort of problem. Also if so do please tell me how you got horizontal span to work on monitors with different resolutions.