Could you please post how many watts at the wall this is pulling... when I did my tests of voltages I could not get the wattage at the wall to change by changing the volts..
I do not have a tool to measure the pull at the wall, but if your tests showed no change, I have no reason to doubt it.
OBITER DICTA: It seems the new firmware that bitmain are testing (I got a copy from bitmain earlier today and you can ask to be sent a copy), handles voltage settings well using the default value of 0000 (I suppose that signifies auto select the voltage). I flashed one of my S3's with the firmware and in the first hour that I was able to observe, it seemed to be handling well. I will not be able to check on the rig as I am away for a couple of days, but will be able to on the 26th or 27th.