What is the combined resolution of your top two monitors? The following code shows how to specify custom position/size of the fullscreen window:
Code:
import viz
viz.setOption('viz.fullscreen.x',0)
viz.setOption('viz.fullscreen.y',0)
viz.setOption('viz.fullscreen.width',2560)
viz.setOption('viz.fullscreen.height',1024)
viz.go(viz.FULLSCREEN)
This code assumes that your desktop origin (0,0) starts at the top left of monitor 1, and that the combined resolution of monitor 1 & 2 is 2560 x 1024. This probably won't work if monitor 1 & 2 are connected to different graphics cards.