Performance (throughput) issue, due to various reason:
Adjustingthe CCA and distance will fine tune the radios to that environment.
The DISTANCE parameter needs to be set (in kilometers) to the length of the radio shot between the bridge pair.
The CCA value needs to start at 62. CCA is Clear Channel Assessment, essentially the establishment of a noise floor below which the bridges will ignore RF inputs, in search of a good, solid signal. The default value should be -62 dBi or 62.
Also ensure you have latest IOS version.