Antenna selected issue

I have installed RB532 with 4 mpci cards. 1 is a Senao 8602 100 mW and 3 CM9.
When Senao with antenna A set, where is attached a Sector antenna, client connected with average of -60 of signal. But ping is very high.
While when I set antenna B where there is nothing attached the client connects with -80 but ping is very stable.
May be I misunderstanding, signal -80 is worst of -60? Why it works better? in both case the noise is -92 db

While CM9 works fine but when I change something on the wireless setting the clients want not connect, and log does not show nothing, only if I reboot the client they will connect.

Best regards