-80~-85 is pretty low, whether or not a link will come up with that will be based on how high the noise floor is, ideally you would want a signal about ~25db above the noise floor, but link should be able to establish as low as 10~15db I would think. You can check the following:
To see noise floor:
show ap arm rf-summary ap-name <ap-name>
To see what channel your AP(s) are on to help with the command above:
show ap active
Ensure that your APs/Radios that are being used for the mesh are trasmitting at or close to max power with the above command as well, if not, tune the ARM profile for your mesh APs to ensure they transmit at close to or at max power.
Hope that helps.
Regards,
Austin