Your in a location that should offer easy, reliable (near 100%) reception.
Two issues...
First - Attic mounted antennas can work well, but can also be plagued with trouble. If your roof is constructed of wood and fiberglass reinforced asphalt shingles, you should usually do alright. If there is metal in front of the antenna, either part of the roof or part of the plumbing, electrical or heating system, you can expect trouble.
My experience with attic mounting has been, wait for bad weather to know what you can really expect. A load of wet snow or ice will absorb an awful lot of signal.
You can try experimenting with different locations in the attic... If you can't find a sweet spot in the attic, the compact CM-4220 would be quite unobtrusive mounted on a chimney or satellite J-pole mount. Any antenna will perform better if it is clear of obstructions.
Second - The CM-4220 is not designed to do much on real channels 7 - 13 and even less on real channels 2 - 6.
KRCW, real CH-5
KGW, real CH-8
KOPB, real CH-10
KPTV, real CH-12
You can add a VHF antenna such as the
Antennacraft CS-600. The output can be merged with the UHF only CM-4220 with an inexpensive UVSJ (UHF / VHF Signal Joiner). Radio Shack Cat. # 15-2586 is a pricey example.
You could also replace the CM-4220 with a
Channel Master CM3016, or an
Antennacraft HD850... that would give you all UHF and VHF channel coverage with no UVSJ needed.