Ok so I finally got around to doing some tests on LR heads. I tested two > 2.6-ohms to make sure the numbers were on par with my earlier test.
I ran through the marked settings 3.3, 3.8, 4.3, and 4.8-V with 3.2, 2.7, 1.7, and 1.5 ohm heads.
With the 1.7-ohm head the voltage was consistent...