XHP50 Current / Voltage Issues, Please Advise

I’m direct driving (18ga wire, springs bypassed, the works) an XHP50 from two 18350’s;
I get 4A at the tail. A bit low in my books.

I try instead with 18650’s;

I check the voltage across the LED (noctigon) terminals with the light switched on;

Looking at this graph:

It should be 6.8V.

This would explain why the direct drive current is fairly low.

What’s causing it?

I am at a loss. I have no idea…