PTP650s co location and crc errors

We have two PTP650S links co located on a tower.  The links are about 90 degrees out from each onter with six feet of vertical separation.  One link is .4 mile and the other is .6 mile.  We ended up using 5.2 and 5.4 to get the  best performance.  Recieve signal in these frequencies is about -57 due to the low EIRP. It seemd the -82 noise floor was  too much in the other channels.  We're seeing more wireless CRC errors on these links then we did on the PTP500's  we replaced.   Is anyone having similar issues with wireless  crc errors?  How many crc errors are too many?