AddExplosionForce() does not appear to have any effect

I'm having hard time with AddExplosionForce() as far as I can tell it has no effect or a negligent effect on the rigidbody.

My scenario is of a top-down 2.5D game, so all rigidbodies have their position Y constrained. In my particular scenario an object explodes and I'm spawning fragments, then I want the fragments to be pushed by the explosion of the original object that blew up.

So my code really is quite simple, a previous piece of code randomly created a few fragments around the object and the relevant piece of code is:

 foreach (var fragment in fragments)
     fragment.rigidbody.AddExplosionForce(BlastForce, transform.position, BlastRadius, 0, ForceMode.Impulse)

If I replace the above code with the following:

 foreach (var fragment in fragments)
 {
     var posToFragmentVector = (fragment.transform.position - transform.position);
     var distance = posToFragmentVector.magnitude;
     var dir      = posToFragmentVector.normalized;
     if (distance < BlastRadius)
         fragment.rigidbody.AddForce(dir * BlastForce * (1 - (distance / BlastRadius)), ForceMode.Impulse);
 }

Essentially doing what AddExplosionForce() advertises, minus the torque, then things work as expected.

I should note that the trigger for this piece of code is from an Update() and not a FixedUpdate(), but since I'm using a single call with ForceMode.Impulse and since ApplyForce() works I don't think that's the problem.

Am I doing something glaringly stupid, or is there something wrong with AddExplosionForce() ?