I just went through and followed the instructions to calibrate the in-camera exposure meter of my Olympus E-M5. I found that the positive exposure compensation was also about 2.3 eV for my camera (for ISO 200), similar to what you reported in your article.

Here's my question: I've been shooting using the in-camera highlights warning set to 245 (10 channels below the upper limit), and set my exposure to the point on my LCD where the warning just begins to show in the part of the image where I want to ensure highlights are not blown out. Obviously, this is all based on the JPEG that the camera creates for LCD viewing. But I process all my images from the RAW data. For the best data, should I ignore the highlight warnings that I've set and use the exposure compensation that I've determined for my camera? Using spot metering or the "full-frame", i.e. Olympus' ESP, metering?

Thanks