Nature's Fury- further confusion

I'm pretty new to LM so this may be basic, but the initial hit of Nature's Fury doesn't deal as much damage as the description lists. All of my other skills work as described, but not this one.

For example:
Lightning Strike is (currently with my setup) listed at minimum 13K - maximum 18K, and always hits within that range.

Nature's Fury is listed at minimum 8K - maximum 12K for the initial hit, but every time I use it, it hits for 5-6K on the initial hit. This is for any enemy; it never seems to hit as hard as described.

I tried to find information about this online but the discussions I found only clarify how the AoE DoT works, not the initial hit failing to do as much damage as described.

As a wild guess, it may be related to the fact that Nature's Fury does frost damage. Maybe you're fighting things with stronger frost mits than lightning mits?