When using a TrackIR while on foot, your view angle is not limited, you can basically turn your head 180 degrees in all directions (to the point that you can look behind but upside-down).

For example, this is me using a TrackIR to look UP. As you notice, I can look "up" by 180 degrees

Additionally, if you press ALT and use the mouse, you can look around 275 degrees, making it possible to look into the stump of your virtual neck.