How to correct the black bars when turning head left & right

[benb0jangles]

Hi there I love alvr :) it greatly improved my msfs and hlAlyx experience on my old setup. But I wish to ask one thing and that is when I turn my head left or right i see vertical black bar creep into frame for a moment then disappear. How can i correct this so that it is always out of frame? Perhaps increase horizontal frame size somehow perhaps? idk.

Thanks