Voltage limit encountered / nVidia M2000M (Maxwell)

In order to stop the GPU fan from being realy loud, I edit vbios in Maxwell II Bios Tweaker (v1.36). I change (1) temp target to 67*C and (2) Voltage table: CLK41 down to CLK32 which refers to clock 1006MHz down to 888MHz in Boost table (I assume that CLKxx values in Voltage Table correspond with Boost table entries - correct me if I'm wrong).
The problem that I experience is that no matter what voltage range I enter in CLK41..CLK32 in voltage table, the real VDDC voltage won't go below 0.9180V when the card performs 3D (games, demos). The card reaches CPU clock 1006MHz and down to 888MHz but voltage is limited at 0.9180V minimum. I checked it by logging in GPU-Z to a file: clock, temperature and VDDC voltage. Even on original VBIOS, the VDDC voltage does not go under 0.9180V in 3D.

My question is how to decrease the bottom limitation of voltage below 0.9180V? Without it, on some hot days the card reduces the clock frequency drastically to obey the temperature target.

I have the rom file dumped in GPU-Z. I view the .rom file in X-Ways WinHex editor but I am not any good in it and I obviously don't know where to modify. Also in Maxwell Bios Tweaker I don't know how to modify for above-mentioned purpose. Please help.