Shouldn't they increase the range of reinforcements?

[Silver Rusher]

Perhaps a delay battle option gives a few days or weeks so both the attacker and defender can get the nearby reinfocements in. Maybe a reinforcement choice that shows your map, the possible reinfocements and lets you and your enemy/allies choose to move them to the battle site.

mfberg

Only the attacker would have this option though.

Yes and also add the option to appeal to your ally/allies for assistance

Brilliant idea.