Yes playing DCS is kind of masochistic when you think about it. You put a lot of time into a single game run (startup-take-off-ingress-delivery etc) but if something goes wrong it is really difficult to tell what went wrong, which might be hugely anti-climatic and frustrating. Yet we all keep returning to it :)
What do you mean by the Bk90 misses its target? Could you provide a track? I can't remember I've seen this issue reported before.
The different behaviors in Bk90 between SP and MP is a limitation with DCS that we are communicating with ED to be able to implement in a satisfactory way. I had to be a bit creative to do the way it's modeled in SP but don't know if you noticed that it also has its limitations (no score for the player).