Can RBE really change voltage to an ATI 4670?

Hi I have just bought an ati 4670 1gb powercolor. In order to maximize the power efficiency I wanted twek the bios with RBE. Prior to do that I wanted to test with ati tray tool frequency and voltage to apply later with RBE to the bios.
The fact is that ATT can't really change the voltage. Even downvolting from 1.2v to 0.9v keeping the 3d frequency of 750mhz the card is stable (which should be impossible such downvolt). Moreover even with such as low voltage the temperature under stress don't change, so my guess is ATT doesn't have any effect on this card regarding the voltage. Can RBE succeed where ATT failed?
All the voltage ATT allowed me to set are the same showed under RBE. I have basically tried all the steps.
I must admit that what makes me pessimistic is that all the default voltage for this card (boot,2d,uvd,3d) are 1.2v..

BAGZZlash said:

It's even simpler. Just load your BIOS into RBE and check if this button ("View/change voltage registers") is enabled:

http://www.techpowerup.com/articles/154/images/RBE_Reg.png

If yes, your card is equipped with a VT1165 and RBE can mod your voltage, if not, then not.

Click to expand...

No, I can't mod my voltage. So I don't understand, why RBE apparently give me the choice the select a range of voltage in step of 0.05 from 0.9 to 1.2 when actually selecting them will no make effect?

BAGZZlash said:

That you should ask ATI. It's the structure of the powerplay table and that's it.

Click to expand...

Well take as suggestion, if you are sure that if the "view/change/voltage register" is disabled then means "no voltage tweak at all can be applied", why don't you make in the next release work RBE so that when this happen the user have no choice of voltage under the frequencies?
That would be clearer for a newbie like me.