Antenna has less than 4dbi gain

I purchased 2 Hawking HAI15SC antennas to improve the performance of my wireless setup. One was to be used on the Access Point and the other for the Client. When I attached the HAI15SC to the Client and pointed it at the Access Point, the performance actually decreased! Emails to techsupport@hawkingtech.com provided no help. Judging by the reviews read online, buy the Hawking HAI15SC at you own peril. It appears to work only in specific situations. It may need large uncluttered walls for signal reflection. As a stand alone antenna, independently mounted, it does not work.

Test Setup: Buffalo WHR-HP-G54 running DD-WRT as a Client Bridge. The Access Point was 400 feet line-of-sight away. Results: Standard Antenna (4dBi omni) – 30% signal quality with SNR of 20, Standard Antenna with parabolic reflector (see freeantennas.com) – 50% signal quality with SNR of 30, Hawking HAI15SC – 20% signal quality with SNR of 15.