One thing to keep in mind is that the RSSI is only an indication of the RF energy detected at the antenna port. The power level reported could be artificially high because it may include energy from background noise and interference as well as the energy from the desired signal. This situation is worst in an interference prone environment where it is possible to get consistently high RSSI readings yet still have communication errors.
If the application is actually attempting to measure "link reliability" and not just "signal strength" it may be helpful to factor in "% packets received" or similar data.
Digi always recommends performing a loopback test and actually measure link performance in terms of signal strength and packet success rate to determine the reliability of an RF system.
Contact Digi support for additional information on this subject.