1D Mark IV Histogram Conservatism

I shot a gymnastics tournament yesterday. I set up my exposure with my new 1D4 as I did before with my 1D3. I shoot in M mode and I generally set my exposure so that I start to see blinkies in the histogram and then back off 1/3 stop. This is my rough-n-ready ETTR method.

Let's pause to cover settings:
RAW capture
Neutral picture style
M mode, exposure set 1/3 stop below appearance of blinkies

So I got home and downloaded my pictures. Everything was about 1 stop underexposed. Everything.

So I shot some test shots here in the family room. Tell me what you think. I think I may have to shoot with blinkies going forward.

This first screen shot was the brightest exposure I could take with no blinkies appearing anywhere on the light switch as viewed on the camera histogram. In LR most of the switch face is ~89, 89, 89 on the RGB.

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The next two exposures are 1/3 and 2/3 stop brighter (1/100 => 1/80 => 1/60).

The camera told me that the entire top and right side of the switch plate was blown out at 1/80. LR says that area is ~ 95,95,95.

The camera told me that the entire switch plate was blown out at 1/60. LR says it is 97,97,97.

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Finally we get agreement between the camera histogram and LR by 1/50. Here the camera was reporting that the entire face of the plate was blown out. LR basically agrees, although it's showing values of 99.8 - 100 over most of the plate.

IMO the 1D Mark IV histogram is being very conservative on warning me about blown areas and it is making me underexpose. What do I do for ETTR? Shift right until I get blinkies and then go 1/3 stop even brighter? It's puzzling.

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Shameless bump, but I'm surprised nobody wants to talk histograms.

Here is an example from the gymnastics tournament. I was all excited to be able to shoot 1/500, f/2.8 and only ISO2000. Then I had to push it one full stop in post and I was less excited. I just don't understand why my manual exposure approach that I've used with the 5D and 1D3 was so far off with the 1D4.

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