Design seismic force is amplified at higher elevations in a building. Best way to describe it is "whipping effect". If your building is, say, five stories with roof height at 60 feet and you have a wall mount unit at 5 feet above seismic base, your hr = 60 feet and hx = 5 feet....
Comparison of Egyptian Code 2012 with Eurocode 8-2013, IBC 2015 and UBC 1997 for seismic analysis of residential shear-walls RC buildings in Egyptdoi:10.1016/J.ASEJ.2018.07.004Ahmed M. El-KholyH. SayedAyman A. ShaheenAin Shams Engineering Journal...