I'm presuming that this is on an IOS based 1252 AP. Gain, when set on an IOS APs radio, only informs a WLSE what the gain of the antenna is for management purposes. It does not affect the actual gain of the antenna.
It's difficult to say why you are experiencing that variation in rates without knowing many more details. I have 1252 and 1142 APs working at various customers that are getting terrific connections.
Transferring Crash file from standby: Login to the Active WLC in HA.
From CLI: (Cisco Controller) >transfer upload datatype crash (Cisco
Controller) >transfer upload filename (Cisco
Controller) >transfer upload mode tftp (Cisco Controller) >transfer
This is the start of a display filter cross reference between Wireshark
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