Target distance is where the target was when you opened fire.... As target approaches (with ~ 300 m/s at least), Tu in seconds is calculated where the target will be....

So if A-4 goes with zero parameter - 3284 meters - (Tu * Speed of A-4): 3284 - 4.2*300 m/s = 3284 - 1260 = 2024 meters....

I don't find a bug here.... Also, some of "bugs" you collect, are not bugs, like:

5, 6, 7...

3 and 4 - cannot understand what you're talking about....