RFID Antenna read at low distance than actual distance

Hi all,
Im using Trovan RFID antenna. There are two types of antenna. 610 and 612. Actually the reader is connected to the antenna. According to trovan 612 antenna read the card tag of distance 80 cm. but my trovan antenna 612 read 40 cm, also the same problem in antenna 610 also, its read at low distance. I checked the connection b\W PCB redaer and antenna, its correct. Then what would be the problem?


Thanks.