Using High Performance User Equipment, Sprint will achieve the coverage of 2.5GHz band which is same as the coverage of 1.9GHz.
Higher frequency band is not good from a viewpoint of coverage because high frequency band is not expected for the penetration and diffraction of radio wave. To avoid it, base stations (like eNB) and User equipment need to have a high power amp for wide coverage. Base station may easy to do it, but it is difficult for UE. If UE has higher performance amp, we concern about energy consumption, affecting human health, and so on.
High performance UE can achieve the wider coverage than UE. I don't know the reason. This article says that HPUE's power consumption is the same as UE's. So HPUE is not only higher transmit power but also other high performance transmit technology (ie. use multiple HARQ).