Those flat-style antennas are a real gimmick, and I wouldn't expect them to work very well in ANY situation. Because of the high signal strengths in your location, any amplified antenna that you use is likely to overload and cause more problems than it solves. You really need a passive-type antenna with some gain of it's own on VHF-high-band plus UHF. Are you adverse to roof or attic-mounting a real antenna? If this was my choice, I would install an AntennaCraft HBU-22 in the attic, or, preferably on the roof aimed at 50 degrees by your compass. The quality and quantity of stations will improve immeasurably.
http://www.antennacraft.net/pdfs/HBU22_.pdf