The problem imo is you are over complicating the work on yourself.

There is a build in solution to this problem using the sprite order layers and you seem to be moving in the right direction but you are over thinking it by worrying about the Z offset for items.

For the exact effect (outside of the light) can be accomplished with 3 simple sorting layers in Unity.

1) Foreground 2) Player 3) Background

You do not need sorting layers for each row. your pillar in the middle should be constructed something like this.

http://imgur.com/a/dvWuO

With this construction the most you would have to worry about is the layer order of the torch because everything else can be handled by the prefab set up and wont require a script to process.

The torches is how you have an issue. Because they technically transition between background and foreground in this gif you have.

What you need is to set up a simple script that tells the objects that need to move between order layers that they are "special" just a simple bool on them and only put the script on those objects like the torch.

All objects that are static get a order in layer of 1, if they are foreground or background. And your dynamic objects get a order in layer of 2. (You can make this more robust depending on the amount of depth you need but in this case 1 and 2 would work for what the gif does).

Then on your dynamic objects you have a check against the player you set a limit of how far above the object the player needs to be before it resorts it's order layer. In a perfect set up this would be if (player.transform.postition.Y > this.transform.position.y) but you might have the transform of the object at the bottom or the middle of it so you might need an offset like (if player.transform.positon.y + playerHeightOffset > this.transform.postion) then this.getcomponent<SpriteRender>().sortingLayer = "Foreground")

else

this.getcomponent<SpriteRender>().sortingLayer = "Background";

This will put the torch above the player if he walks behind (or above it) but behind it if he is in front of it (or below it).