Well now I had a chance to play around with this some more last night and today, and at least on my phone...so far...I seem to have found something.
Regardless of phone orientation, when I enable In-Pocket Protection and put it in my pocket it DOES work...until the first time that I manually blank the screen with the power button. From then on it will NEVER work, until I go to Settings to disable and re-enable. Then again it will work always, until I forget and manually kill via power button. I have now done as many as 30 in-and-out of pocket, after and while running various apps, and the protection always works...until I forget and manually use the power button to turn off.
So now it seems to work great, as long as I am willing to let the screen time out on it's own when I set it on a desk or something. In order to save battery I normally would not want to do this with my 2 minute time out, but I have had mostly decent success holding the phone against my chest for a moment to simulate going into the pocket. The key there seems to be having the entire face well covered.
Give it a try.