W520 temperature sensor oddity

[Colonel O'Neill]

On the W520, does anyone know what the gpu sensor in TPFanControl represents exactly? It seems to deviate (higher) from the GPU temperature read by all other programs (HWMonitor, NVIDIA Inspector, GPUTool, Furmark, MSI Afterburner, etc.):

https://i.imgur.com/lUFqwEs.jpg

(Bit of an old pic, but it still mostly applies.)

The GPU throttles as soon as the TPFanControl value exceeds 100C. The temperature difference also differs under different workloads, and is highest under FurMark.

At first I thought it was the VRAM, which wasn't heatsinked. Applying thermal paste to the VRAM reduced the temperature reading marginally, and allowed me to up my GPU memory clock by 11 MHz from 1080MHz to 1091MHz (900 MHz stock). Looks like it's not it.

Anyone have any ideas?