I would print out the health value along with the damage, because I don’t see why it shouldn’t decrease. I think it’s more likely that your “kill-event” doesn’t trigger or your health gets reset somewhere else. But I can just guess from here.
Then I would get rid of the component you use for the radial impulse and add a node “AddRadialImpulse” to the OnHit-event of the rocket, because you only need it once on explosion and you can easily set the same parameters (like radius) for damage and impulse nodes.
Have you made the outer radius larger than the inner radius? I would do that, because you don’t know what the engine does with these values internally when they don’t “fit” together.