The last sentence is very funny! It's implemented as what's the easiest to do currently. When the unit is on a wall, he has a state of being "turreted", this is what boost his defenses. When not, it doesn't have any bonuses, regardless of if he is behind a wall or whatever. The projectiles make their lives without ever acknowledging walls. For sure would be nice to have this enhanced. You are right that bridges might have similarities with potential bridges (entities, not terrain as currently is) about how we could build them. But there aren't anything supporting walking across them currently. Units don't walk on fields, they just don't get any obstruction from them, so they actually walk on the ground.  So yes, not really a simple task to get this into the game.

@OutisWalking on top of walls along their extent while being a bit protected could indeed be an interesting side-effect. Which brings me to a (most likely stupid) question: A soldier positioned on a wall has some protection against enemy fire. I the same soldier is behin that wall, does he have the same level of pretection, more protection, or less protection?  From my simple mind I would guess being behind a wall shoudl provide more protection. Most likely implemented as expected. Can anyone confirm, please?  

Yeah I've updated the scripts and ported that mod to test. I need to publish 28.1 on mod.io

That looks very well

I use formations only to group my army better before the attack. Note that there are some serious bugs with formations. If you add an unit that is very far away, the entire formation stops and waits for that unit to get near. Also, if you attack move with the formation active, only some of your units will move in to attack.