Yea, but so many of us 'experts' like to snow the newcomers (and impress our peers) to make any subject or question from a beginner to be as confusing and irrelevant as possible. It's what we do as a hobby and our hobbies make us happier in life.
Lefty
Well, I guess you could include average junction temperature, operating environment (To include season, prevailing winds, climatic variances, global warming coefficient, and magnetic correction), as well as the heat generated by the proximity of the end user. If the project is in dairy country, may need to add a correction factor to the global warming coefficient as well.