prefab instantiation not on same horizantal plane,Improper placement of prefabs

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();
     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