Here is the truth about outdoor Tv antennas.
http://www.fcc.gov/mb/facts/otard.html. Outdoor antennas are , handsome , pretty , and very good looking. . The signals at your location are Very Strong , the multipath environment of the attic is likley overloading the tuner with to much Very Strong multipath. Adding a amplifier will make the situation even worse. Amplifiers amplify the multipath also.