Option for capital placement or just more reasonable default placement about feudaltactics

[Sesu8642]

Playing the new capital close to where the old one was indeed keeps it in the "danger zone". This somewhat forces the attacked player to defend it better in the next turn (if they can). Destroying the capital over and over again can be a strategy to defeat a player with a larger kingdom than you have. And indeed if you relied on the capital protecting your tiles, the new one still protects some of the same tiles.
When a kingdom is split, the new capital should be placed randomly. What you observed was probably a coincidence.
Making the logic configurable by the player, could be frustrating because you'd have some control but there will always be situations in which the placement would be undesirable.
But I think it is indeed a good idea to remove the randomness. I'd have to play around with your ideas to see what works.