The current implementation ISE uses in the Arma games basically relies on mapping your gaze point on the screen to a camera rotation. This means that you need to map the distance from the center of the screen to your gaze point to an angle between 0 and the maximum view angle. If the distance from the center of your screen to the edge of the screen is 20 cm then that would mean that 1 cm would correspond to 180/20 = 9° rotation! So while it’s theoretically possible to increase the max angle to 180°, it’s simply not feasible since it would make the view extremely sensitive and also because the error margin of the actual eye tracking alone (which might vary quite a lot between persons and setups) would cause the view to shake.
We are currently working on some pretty cool stuff for ISE which will solve this problem in the future but I’m afraid I can’t go into details right now. Stayed tuned 🙂