We have added quite a few tools to LP360 (Standalone) aimed at small unmanned aerial systems (sUAS) data processing (and small area LIDAR, of course). Here are a few tips for defining stockpile toes for volumetric computations.
You will note that the automatic toe extraction Point Cloud Task (LP360 Advanced or Topolyst) has an option for Overhead Points. When selected, this algorithm attempts to segregate overhead points from stockpile points. The classic example, of course, is an overhead conveyor. It is important to note that checking this option when you do have overhead structures aides the algorithm in finding the toe, even if you are not interested in classifying the overhead points.