The concept behind tilting the glass slightly (industry has anywhere between 3-7 degrees per pane) is to avoid having either a trace light reflection going directly back into the lens. Although this issue is minimal when using the OptiClear Anti Reflective glass, there is still a minute amount reflection. A tilt is used for extra effort to have as much clarity as possible, although it can rarely be noticed with an untrained eye if you are unable to tilt at all.