I written an answer to this in what follows:
(From my website, http://www.t-lea.net, written by myself.)
What do you think? This may not exactly be Philosophy of Science, but it may represent an example in its way of reflecting something of science in a philosophical way, in a sense, the very making of the science.Explantion: optimal temperature happens a little outside the surface of the corona because the atoms/particles have greater space for temperature vibrations there according to this optimal temperature of these circumstances, the atoms/particles being held to the Sun, a little outside the corona in this fashion. Temperature should indicate something about the space between atoms/particles because temperature corresponds to the (propositional) excitation/vibration of the atoms/particles.
If one would have the same temperature farther in toward the Sun's core then it has necessarily the same, relatively thin composition there as well, you know, this being a smaller Sun, even if the mass in this case either has to differently organised relatively to the substances of the Sun's composition or that it's just lighter.
The conclusion is that the heat (or superheat) is optimal a little farther out for these atoms'/particles' vibrations to produce this heat than where atoms'/particles' become more dense as one moves in toward the core of the Sun. I'm uncertain to what degree this may hold, describing the variations of the temperature of the star at all levels, but this explanation/theory is, of course, meant to hold for conditions of hot surfaces on all instances of the kind our Sun is displaying. So it's first and foremost an explanation/theory of description that applies to this surface and its gaseous outer layer, but it may also extend to, in a variable manner, a host of conditions of (astro-)physics.