It must have a chip inside that's capable of recognizing an aircraft's shape. It's pretty easy to make when you think about it, it's just image recognition sotware.
You have to understand that we, the average Joe, really don't know much about the capabilities of the missile in real life. So making a statement that it should be that way or this way just isn't reasonnable.
I'm not saying the weapons in DCS are perfect but the thing is, without any proof or any data to support your statement you have to consider that there's a very high chance of it being false.