Too much is when you are breaking EIRP limits
Or if your radio does not have enough bandwidth in the front end, and it over-loads the hell out of it. If this is the case then you probably should switch manufacturers.
If you are very close, naturally in those instances one should use proper judgement.
30-35 above your receive sensitivity. In my experience this has been around -60dB, but this is all relative as it depends on the equipment you are using. You can, it seems bend the rules depending on the radio system involved.
I should also add that one might consider other environmental factors such as dust storms. It is fairly dry where we are, but we had two dust storms last summer that knocked an old microwave system off the air. I do not know of when the system was last PM'd, so it may be that the antenna system needs checking.--
"No job is so important, and no service is so urgent that we cannot take the time to do it safely."