Okay, this is puzzling.
Here is a very simple situation and it won't take more than a minute or two for you to look at.
The SAG has fired some SM-3 IIA missiles (already in the air) at some incoming DF-21s. thanks to lots of radar units, the missiles were detected far away. The intercept is going to occur about 600 miles away from the SAG. The incoming missiles will be almost at 300 km above earth when they are intercepted.
The SM-3s missiles climb and climb and will intercept them something like 4 times in a row with no problem. Then, on maybe the fifth time, they will not reach the altitude, and every missile will "UNDERSHOOT" (it will say "OVERSHOOT") their targets and everyone will miss. Start the battle again, and the next time they will all hit. Try it a few more times and they will likely all hit, until you get another result where they all UNDERSHOOT the targets again.
This is the SAME scenario, and the same missiles, and the same calculations. I can't see a reason for this.
The biggest issue is there is no time for any further shooting, and a miss is as good as a death sentence. So, it is a concern.
Please, to everyone, try it out five times or so. See if you have the same results. It really won't take but about five or six minutes of your time.