collision direction( top, bottom, left, right)?

Unity Engine
1

I want to know how can I check the collision from different directions.
Let me explain it a little bit; I want to check the collision between my bullet and a platform object from 4 different sides( right, left, top , bottom)
I know I can use 4 different colliders, but there should be a better solution.

I can check the right and the left side, but when I try to include top and bottom everything gets confusing

here is the collision function for right and left edges of the platform;

if(transform.position.x < collision.contacts[0].point.x || 
   transform.position.x > collision.contacts[0].point.x)
   {
       ballVelocity = Vector3.Reflect (ballVelocity,Vector3.right);
       transform.rotation = Quaternion.LookRotation(ballVelocity);
   }
2

I got it figured out. it doesn’t feel like it is the best solution, but works fine.
Here is the script if someone ever needs it…

        if(collision.gameObject.tag == "Platform")
        {
        	if((transform.position.x < collision.gameObject.transform.position.x  
        	collision.gameObject.transform.position.x-transform.position.x > 1.5) || 
        	(transform.position.x > collision.contacts[0].point.x 
        	transform.position.x-collision.gameObject.transform.position.x > 1.5))
        	{
        		
        		ballVelocity = Vector3.Reflect (ballVelocity,Vector3.right);
				transform.rotation = Quaternion.LookRotation(ballVelocity);
        	}
        	else
                {
        	ballVelocity = Vector3.Reflect (ballVelocity,Vector3.forward);
		transform.rotation = Quaternion.LookRotation(ballVelocity);
                }
        }