If you are talking about the newer CM4228HD (horizontal rods as reflector), then Ken has a separate page describing how the phasing lines between the two halves of the antenna ruin its performance:
http://www.hdtvprimer.com/ANTENNAS/TemporaryPage.html
The old 4228 (wire mesh as reflector)
was actually better than the 4221, but that's no longer the case now that the design has been changed.