I have to say that I have noticed this type of atmospheric distortion far more with the XH-A1 than I did in 5 years using an XM1, with a similar zoom range. I do wonder if there's something about the MPEG2 encoding that exaggerates the effect a little?

I was thinking more of HD resolution exaggerating this effect.
In the past I've have shot quite a lot of nature ranging from Canada to New Zealand with a Sony 2100 and never notices this before exept in hot places.