On August 12, 2015 the FCC granted a waiver (pdf) of some Part 15 rules to allow iRobot to market a robotic lawn mower transmitting in the 6240-6740 MHz range (Order in Proceeding 15-30). The National Radio Astronomy Observatory (NRAO) had expressed concern that the waiver could lead to interference to radio astronomy operations.
The Office of Engineering and Technology noted in its waiver grant that "because the NRAO analysis looked at line-of-sight separation distances, it has greatly overestimated the interference potential of transmitters that are located less than two feet above the ground."
It added, "We find that when taking into account the variability in propagation characteristics due to terrain, low antenna heights and other propagation factors, grant of this waiver is very unlikely to increase the potential for harmful interference."
The glass-half-full reading is that the FCC rejected a worst-case analysis; the glass-half-empty view is that it missed an opportunity to do a probabilistic risk analysis that quantified expressions like "greatly overestimated the interference potential" and "very unlikely to increase the potential for harmful interference."
The cynic's take is that this is to be expected; providing hard numbers would expose the Commission to having its reasoning questioned during subsequent litigation.