prefabs not aligned at same horizantal level after instantiating

Question

I have generated a logical grid and trying to place a prefab on top of that grid.

Piece is the base class for all pieces

Pieces[] is the 2d array holding all the pieces

1. instantiate and spawn prefab

private Piece spwanSinglePiece() {

 Piece cp = Instantiate(prefabs[0], transform, false).GetComponent<Piece>();
return cp
}

2. Position them

  private void PositionSinglePiece(int x, int y, bool force = false)
    {
      
        

        Pieces[x, y].transform.position = GetTileCenter(x, y);



    }
    private Vector3 GetTileCenter(int x, int y)
    {
        return  new Vector3(x * tileSize, (float)(yOffSet +0.85), y * tileSize) - bounds + new Vector3(tileSize/2,0,tileSize/2);
    }

Scenario

1. only yoffset value is helpful to place them on top of the board
2. but different prefab pieces require different yoffset value. cause after instantiating they are not on the same base
3. board scale is set to 1,1,1 so that parenting doesn't scale the pieces along with it
4. created prefabs scale is also 1.

Problem prefabs are not exactly on the same horizontal alignment. which is resulting in the use of different yoffset values for each piece.

if all the pieces are aligned horizontally same they single yoffset value can work this what I am trying to achieve

More details

original prefabs transform

clone prefab generated after running script. every clone prefab has a y transform of 1.05 after being generated. which is expected but all prefabs are not on same horizontal line.

so they are in different vertical position. I am not sure what really causing a issue

update - using primitive objects, scripts just run fine and produce expected results.

I think its a problem with the pieces that were created in the blender and exported into Unity

 1. after creating the mesh, rotating and scale applied 
 2. centred origin to geometry and pivot to the median point
 3. normals recalculated
 4. while exporting settings where as follows

Answer 1

It's possible that the models were not properly aligned in the 3d modeling program used to create them.

The ideal solution would of course be to tell the art department to get back to their 3d modeling program and move the meshes within their model files so that the floor is on height 0. This is usually a standard convention for game-ready 3d assets which are designed to be placed on a horizontal surface.

But when you got the assets from a source you can't make demands to, then you can fix this in Unity.

Create each piece prefab as an empty game-object with the 3d model as a child. You can now edit the prefab and adjust the local position of the child transform relative to the parent transform so that the base is exactly on the 0:0:0 point of the parent.

Answer 2

Your GetTileCenter() seems to be taking the mid points (horizontal & vertical), but from the image, it looks like each of the prefab have different height, so even though their midpoint is alligned, because of height, it looks uneven.

For height, you can rather use the top position, new Vector3(tileSize/2,0,0);