Castles don't stop armies from advancing, right ?

[B0rsuk]

If I'm not mistaken, it works this way:

If an army sits on a province with castle, but castle is held by enemy, the besieging army can still move into enemy territory.

I think it's a bit unrealistic and disappointing. At least some castle types should either stop armies from advancing into enemy territory or... something like attacks of opportunity. I mean, if I keep the castle and the army goes further into my territory, I should have an opportunity to easily attack it from castle.

In other words, If I send an attack from my castle on an army which was there last turn, I should get movement priority.

What's the point of Jarvellan Wall, anyway ? It would make sense for it to stop armies from going into enemy territory (the only option would be to retreat into your own territory unless there isn't one).