Discontinuity in eHata during radial calculations

[wkozmaNTIA]

This issue was originally brought forth by Andy Clegg. In version 1.0 of eHata, a radial calculation could result in non-intuitive discontinuity due to the 3-15 km region. Paul McKenna proposed a solution which used a different blending function and kept with standard propagation modeling practices. This issue is to implement that update in the software implementation.