What do you mean by "overhead fire", friendly units under the trajectory? What about danger close fire missions? It's been over two decades since I was junior enlisted FDC.
I have placed steel on target with a 81mm and watch the next three rounds walk off the target. All 4 were from the same tube with absolutly no change in the data sent to the tubes.
BY the way OIF retaught all the crunchies and CDATS that Artillery is the "KING" when they found out that they could prep the objective and have very little left to fight them. This is coming out in AAR/Lessons Learned form OIF.