End Element of a ElementRange

First, here is a picture to illustrate what I am trying to do:

Given an ElementRange, I am trying to find the upper and lower boundaries of that range, as in the FP_LocY values (show visually in yellow). The upper value is easy, because I can get the top element in the ElementRange. But I am not sure the best approach for getting the lower value. Any help will be appreciated. Thanks.

-Rick