Right off the bat, and once again, I don't have P3D, but looking at the HUD and two DDI's it looks to me like you locked onto the target past the one that's closest to you. That's why, when you shoot, it LOOKS like the rounds are going under your tgt. They're aimed at the next target, not the closest one to you. Again, this is ALL "it appears to me as though"...
I know it's very difficult to duplicate a situation like this, so you may not be able to re-try this particular scenario.
Try this, if the same situation arises again: When you lock up a tgt, switch the radar to ST mode, upper left corner. Click the soft button twice from RW mode to get ST mode. That way, the radar will only display one target. Only the one you have locked up. Also, lower the radar's range to 5 mi, to get more detail of the close-up targets, so you can be certain you're locked to the target you actually want. You should also only get one TD box on the HUD in ST mode, and all the ranging information, the circle showing range and Vc and so on will be on the one target you want.
Hope this is some help...
Pat☺