I probably don't have much useful information or able to help much as I have only experienced this phenomena on the 146MHz and 446MHz amateur radio bands. I have never tried it higher than that as I don't have the equipment in my shack for the frequencies in which my license covers. Both instances experienced were tropospheric level ducting due to just the right weather conditions and were not repeatable. I know a few guys that play in the microwave band (~1.24GHz); but their signals are mainly line of site, there are no ducting effects that I'm aware of, but I'm not familiar enough with that band to really have a good feeling for it.
Since you are dealing with commercial band services and different power output levels, I don't know how ducting will affect your service. I think it would depend on the antenna gains of your equipment, transmit power and the antenna location.
I thought cell sites were typically 5w or less to avoid any possible interference affects; but I may be wrong on that output number and thought process.
You may want to search for tropospheric ducting and see if there's any information there that may help you answer your questions. Good luck.