What to shoot for with respect to pH and how to measure it had been very confusing to me which is why I did spend quite some time in looking into this. This is what I found.
pH targets and optima are generally given at room temp. As a result it is good practice to only test the pH of a room temp sample which is also prolongs the life of pH meter probes.
The pH measurement with a pH meter is affected by both the pH shift in the sample and a change in the pH probe's response to pH. The latter is what ATC meters correct for. This leaves the temperature pH shift in the sample which is genuine change in the H+ concentration and pH meters cannot correct for it since this pH shift depends on the chemical composition of the sample.
To answer Gordon's question, all ATC meters use whatever curve is needed to report the correct pH regardless of temperature. In the end they probably use the same cure since they all use a glass electrode.
If all measurements are taken at room temp and if pH data in the literature is reported at room temp the pH shift in the sample does not matter which is why I don't think it is at all important if the shift between room and mash temp is 0.35 or 0.22. This is why I also think why a brewer's pH meter doesn't need an ATC function.
I checked Brigg's Malting and Brewing Science again and here is the page that talks about the temperature depended pH shift: Google Books
Looks like he references a source that did that experiment. I should run my experiment again and record what I did. It's just that I don't like subjecting my pH meter to high temperatures.
For those interested, here is some info about pH meters and what I found useful features: pH meter buying guide
Here is some info about mash pH and temperature: http://braukaiser.com/wiki/index.php/Starch_Conversion#pH_and_brewing_water
. To be honest, I also quote the 0.35 correction there. Most likely b/c I got it from Briggs and the experiment that showed 0.22 was done after I wrote that article.