UniWB - ETTR - how to check difference raw&jpg clipping?

I managed to set UniWB on my 5Ds R and would like to see how big the exposure difference between jpg clipping and raw clipping is.

Strangely, images that seem to clip a lot on the camera (only green) show a histogram which hardly clips (both raw & the internal jpg extracted using QuickJpegFromCR2). The contast, sharpening and saturation are all set to lowest value in the picture style 'neutral' in my cameras menu.

I use ACR to check the histrograms, could that be the source of the difference in histogram appearance between ACR and the back of the camera? Any suggestions how to check/measure it approximately?