Thanks for posting the link to your report.
Do you have the model number of the antenna? Is it this:
http://www.walmart.com/ip/RCA-Suburb...-Mast/10828410 ?
When you look at the numbers for WXIA: Real CH-10, Noise Margin 26.6 dB, 2EDGE Path & Azimuth stand out as the most informative pieces of information.
More than the UHF band, the VHF band is affected by noise from motors, computers, engine ignition systems and similar sources. So, your report that VHF signals are affected more than UHF is not a surprise.
You say the antenna is in the attic. Attics can be fair locations for an antenna, they can also be quite troublesome. If there is a device in your home that's generating interference, the antenna in the attic is going to be influenced much more than if it were outside, above the roof, clear of obstructions. A roof can attenuate TV signals a few dB or more than 20 dB depending on what the roof is made of. A wet roof is going to attenuate more than the same roof that's dry.
Airplanes don't need to pass through your 'shot' to cause trouble. By reflecting the signal it can produce a phenomena called multipath interference. Your tuner has a more difficult time recovering error free data when the direct signal from the TV transmitter is mixed with another version of the signal that traveled to some reflective object (an airplane for example) then to the antenna... the two signal may add together, increasing the strength of the signal, but just as likely, they may be out of phase... working in opposition, thus cancelling each other. When the reflective object is in motion, you are guarantied the signals will rapidly fluctuate between adding and cancelling each other. This is because the length of the reflected signal path is changing, so the phase relationship also changes.
Then, there's the problems caused by terrain blocking your view of the transmitting antenna. The 1 or 2EDGE path is indicating this is the case for many of the signals. The signals are scattered much the same way sunlight scatters just before sunrise and just after sunset. (There is some light, but far less than when the sun is above the horizon, and the light is diffused, that is, light arrives from more than one direction.) The tuner is affected much the same way as in the case of multipath as described above.
The bottom line is, You could be seeing more stations, more reliably if you mounted a high gain antenna with a clear view pointed toward 135° compass. I'd suggest a Winegard HD7698P. If you have more than 20' of coax, or any splitters, add an Antennas Direct CPA-19 preamp.
The 7698 is rather directional so it's better able to receive more signal from the direction it's pointed at, while receiving less interference from the other directions. This addresses the problem of weak signals as well as multipath. Mounting above the roof uses both the additional distance and the attenuation of the roof deck to reduce the amount of interference from inside the house received by the antenna.
If you can't afford another antenna, the existing antenna will do better if mounted outside, clear of obstructions. The CPA-19 preamp like all other amplifiers is capable of 'pushing' signal through the coax and splitter that are on the output of the amplifier... Amplifiers can not 'pull' signal from an antenna or out of the air.