Calculating distances: where's the error?

I have two movable objects. At the press of a button, I create the vector "distance" between them and get it's magnitude. Then I move a disabled box collider to the point halfway between those two objects (objectA.transform.position - distance.magnitude/2), rotate it appropriately and enable the collider. So far so good.

Now, when I set the collider's size (distance.magnitude/2, someValue), something weird happens: when the two objects are close together, the collider is too small, when the objects are far apart it's too large, reaching beyond the objects' origins. I expected the collider to extend always from one object's transform position to the other's.

 distance = new Vector3 (playerA.transform.position.x -playerB.transform.position.x, playerA.transform.position.y -playerB.transform.position.y, playerA.transform.position.z -playerB.transform.position.z);
 
 //setting the collider's position halwfway between A & B
 linkObject.transform.position = (playerA.transform.position - distance / 2);
 
 // rotating collider
 float angle = Vector3.Angle (distance, Vector3.right);
 float sign = (Vector3.Dot (distance, Vector3.down) > 0.0f) ? -1.0f : 1.0f;
 float finalAngle = sign * angle;
 linkObject.transform.eulerAngles = new Vector3 (0f, 0f, finalAngle);
 
 //this is the bit I don't understand why it doesn't work
 boxCollider2D.size = new Vector2 (distance.magnitude / 2, 0.5f);
 
 //scaling this doesn't work correctly either, btw
 linkObject.transform.localScale = new Vector3 (distance.magnitude , 0.1f, 0.1f);  

What am I missing?