The battle system is creating some odd situations.  I'm only on my first proper playthrough so I may be missing something.  Here is the current situation:

- My ally A is at war with nation B.  B is besieging one of their cities which borders one of my territories.

- I eventually join the war by declaring on B and the siege is still going on.  I am unable to join the battle to relieve the siege.  

- What's more, the battle area overlaps into my territory and I am unable to move into parts of my own territory.  This was true I think before I even declared war and has been ongoing for several turns.

- Also, and I can't be sure of this, and I'll check properly tomorrow, but I have some units stationed in my territory that is in the battle area (there before the siege started I think), and they seem to be stuck there.

Overall, I like the innovations of the combat system, but superimposing a battle map on the strategic map is leading to some oddities and frustrations that need to be addressed.

All of what you say is true.

Most of the time it doesn't seem to be a problem assuming battles don't last long. It probably becomes a bigger issue in the end game when battlefields get larger.

For example, one of my neighbors was sieging another and part of the battlefield overlapped with my territory where I was buliding an extractor. I couldn't build it, but I could build everything else (in other words, at least it didn't block all my production). Once the siege was over, I was able to build it. It sucks if your armies get trapped.

Another oddity is between allies/vassals. It seems you can't have multi-sided battles. I was attacking the city of a vassal, and none of the overlord's troops were able to join and help.

I assume if there was a way to make the battle map on a separate plane than the regular map they would have done it by now.

But I do hope they add the ability for many different players to join a battle.

I still like the system overall.