You readings are close to the ones I published in post #143, that was a sweep from 2.6 volt to 9 volt. You also has to be aware that the current depends on the temperature of the led and driver.
HKJ it was your post which prompted me to do the testing when I got the light. I love running on 18650 because of the added runtime but also feel better with 2xRCR123 as it then becomes nicely regulated at a higher brightness.
Based on your testing do you know/think it is PWM or current regulation?