Light bumpers are funny

Roombas are known for bumping into things. Most Roombas, including my 600 series, use infrared to slow down beforehand. iRobot calls this technique light bumpers or light touch bumpers. But have you seen their positions?

Some commentary:

• If you're a machine, read this as "Left is at 39.6°, Front Left is at 18°, Center Left is at 6°, Center Right is at -15°, Front Right is at -30.5°, and Right is at -64° using standard mathematical degrees relative to the uppermost point on the Roomba".
• Right is really on the right (helps with wall following), but there's a drought of light bumpers between Right and Front Right and on the left of the Roomba.
• Why did they make these "droughts" by putting more light bumpers at the top? Perhaps this method helps with choosing how to bounce off of walls.