When Is A Siege Not A Siege?

[mano'world]

I'm currently playing April '61 scenario as CSA and as usual (well OK I've played it once before so this is the second time) I'm getting hammered in Virginia (it's December '62 now btw) leure: .
The point is that at Fredericksburg I have Magruder INSIDE the city and Beauregard's Army of the Potomac with T Holmes' Corps in the same region but NOT inside the city. Nonetheless, there is a Union force in the region which is, according to the symbols on the map, besieging Fredericksburg. Now, if I have undefeated units outside the city how can he be besieging the city without there being some sort of battle to decide who's controlling the countryside. Admittedly there have been alot of battles going on in the area so it's all a bit fluid and may get sorted out in the next couple of turns. Nonetheless, I would appreciate a couple of comments from those who know all about this apparent contradiction.
Ta,

[Jabberwock]

Are Bory & Theophilus both passive? Try changing their posture.

[mano'world]

Jabberwock, thanks for the response.
Yes, they were both active as I recall. Admittedly things have moved on from then and the siege has been lifted as The Union continue their apparent random manouvres across Virginia. But I was just querying the apparent anomoly of having a siege going on in the same region as 'in the field' formations.
Next time it happens, tho, I'll check everybody's status.

[arsan]

If both sides stacks are on defensive or passive and both have more tah a 5% military control on the region there will be no battle. They are warily looking at each other camp.
One of the both will have to take the offensive and attack the other to get a battle!
Bear in mind the regions are quite big. More than enough to accommodate two armies inside.
Regards!