The calculation is based on the methods presented in:

"EM61-MK2 Response of Standard Munitions Items," NRL/MR/6110--08-9155, October 2008  

"EM61-MK2 Response of Three Munitions Surrogates," NRL/MR/6110--09-9183, March 2009  

The responses as a function of depth can be calculated for items in their least favorable orientation and their most favorable orientation. Thus, the curves bound the response to be expected for an item at an arbitrary depth and orientation.