Channel Fly should help determine best channels in your environment, based on individual AP measurements of the RF around them.
They should settle down on some desired channels after a few days, when many customers will fix the channels. That should help to
optimize your coverage on both bands.
Then, if you see sub-optimal performance, you need to analyse the client devices performance, affected by their distance from the AP
and interference local to them. You see connected client RF stats in the AP support info file. A "good" connection will have PER < 10,
and RSSI - PER >= 25. The RSSI is relative to client distance from the AP, and packet error rate indicates RF interference near the client.
example: client (STA) has RSSI = 24, PER = 7, fairly good signal strength, only 7% packet loss, getting 54mbps data rate.
STA: c4:10:8a:df:b7:c7
rx_data_frm 946619 rx_mgt_frm 2541 rx_bytes 338562247 rx_dup 702
tx_data_frm 1923183 tx_mgmt_frm 2541 tx_bytes 183424615
good_tx_frms 1925724 good_rx_frms 949160 tx_retries 597084
tx_rate 54000 tx_kbps 5234 rx_crc_errs 49292
tx_per 7 ack_rssi 24 rx_rssi 24
If you identify a few clients that show high PER, try to find where they are sitting/standing as there may be some source of interference.
If you identify a few clients that have low RSSI, try to find where they are sitting/standing and if there are any walls/barriers between them
and the nearest AP(s)? The type of WLAN (hidden/visible) doesn't matter.