Front Wheels w/ Low Angle Center
The Low Angle center is 2 inches deep through the windows (front to back). This is necessary for narrow or shallow wheels when putting the center as far forward as possible. This gives maximum fender clearance and is usually used for front wheels. The front side setting will be minimum.
Rear Wheels w/ High Angle Center
The High Angle center is 3-1/2" deep through the windows (front to back). The wide thicker center curves much further out giving a deeper bowl appearance. Because of its width, it can only be made in 8" or wider widths. The wider the rim the more offset variation is available.
E-T Wheels Tips (PDF)