I've been toying with quake mode and noticed some odd behaviors when running on multiple monitors, where one is on a vertical orientation. On first summon quake mode dropped down from my desired "main" monitor. Consecutive summons have it split between two monitors but never on a single monitor. I tried changing the monitor and desktop values of the command without luck.

In the attached image you can see that the window dropped down to my left most monitor (which is vertical).
It appears the drop down is tracing location of mouse relative to left|right of center in regards to the entire resolution of the combined screens (?).

If my mouse is towards left of center it will render on left most monitor, with the right edge meeting center of main screen.

If my mouse is to the right of center of main screen it renders on the right "half" of the resolution, with the left edge meeting center of main monitor.

Last interesting thing to happen is -- if my mouse is on the left edge of my left most screen it renders off screen.