Thank you for your reply!
Yes, you're right, the default value for machConvectionFactor is exactly 1.72, but I'm talking about the value found in debug menu - Physics - Thermal (though I don't know whether these two are the same or not). You can see my menu data on the screenshot: http://imgur.com/a/ftZwu
And if they are the same coefficients and my installation is indeed corrupt, where should I place this config file and how should I name it?