Look at the AP Support Info file, saved while you have a bunch of clients. Under the WLAN correspoding
to your SSIDs, you can see connected client statistics by MAC address, like this:
STA: 28:92:4a:bb:d1:4c
rx_data_frm 107 rx_mgt_frm 4 rx_bytes 59649 rx_dup 1
tx_data_frm 23 tx_mgmt_frm 6 tx_bytes 2198
tx_assoc 2 tx_auth 1
good_tx_frms 29 good_rx_frms 111 tx_retries 1
tx_rate 48000 rx_crc_errs 31
ack_rssi 32 rx_rssi 41
STA: e0:75:7d:61:6a:59
rx_data_frm 134 rx_mgt_frm 7 rx_bytes 16493 rx_dup 1
tx_data_frm 124 tx_mgmt_frm 9 tx_bytes 26648
tx_assoc 1 tx_auth 1
good_tx_frms 133 good_rx_frms 141 tx_retries 41
tx_rate 39000 tx_kbps 8616
tx_per 40 ack_rssi 22 rx_rssi 21
A "good" client connection should have PER (packet error rate) < 10%, and RSSI - PER >= 25.
User number one has a strong RSSI of 41 and no PER, equals a good connection.
User number two has only 21 RSSI (may be greater distance from AP), and a PER of 40 (bad, indicates
an interference source near to this client). These stats also show more retries by user number two.