The IBM Poughkeepsie EDACS system is quite limited in power. In fact it was common to be out of range while working at the Boardman Road buildings about 2 miles away.
I know for Poughkeepsie the radio tower sits in the area behind Building 052 on the main site. Not sure where the E Fishkill radio tower is. There were never any issues with interference between Poughkeepsie and East Fishkill.
I can only speak for Poughkeepsie, when I was there the 911 UHF links were not full time. The control center operator had to patch them together. They were hardly ever used. The UHF links that were full time were IBM-450 (462.3250) so AFD could monitor and communicate with EC, AFD EMS (463.1250), and AFD F/G (460.2000) both of which were seldom used and we were encouraged not to use them.
Most comms between AFD and IBM EC happened right on the E/C Talk Group which was linked to the IBM-450 Talk Group and thus 462.325. This UHF freq is the only radio access AFD has to IBM. AFD does not have EDACS equipment.
The Fire Dispatch, Response, MED 9 links were hardly ever used. Anytime IBM EC needs to communicate with DC 911 they use the UHF mobiles and portables.
Times have changed, there has been a lot of transition and change with leadership and operations at least in Poughkeepsie, so some of the links may be full time now.