Which tuning do I use? Why do I settle with relative tuning (will explain) and not always match the exact frequencies?

The simple answer is, because i play alone most of the time and there is no need for me to have absolute frequencies.

The tuning relations

I use standard tuned guitar to play Indian Raga songs – Carnatic or Hindustani, play chords and chord melody etc.

I follow the tuning relations when tuning the guitar so that the keyboard has the kind of patterns like shown at that link.

I usually stay in the range of the absolute tuning frequencies, but don’t mind a little up or down. At times I may even tune down the strings a little bit so that I can reach some high notes more comfortable.

At times a little high, so that if the pitch is A, I am not touching the low low of my voice…

You see, I am just using what is enough for my needs. 

If we look into music, even in Carnatic, the original lessons being taught in Mayamalavagowla has been attributed to the practical advantages it has when a child started playing Veena. Again, Veena was one of the two most important instruments and the tradition stuck. (search Prince Rama Varma Mayamalavagowla in youtube)

Later theories started saying how the masters thought hard and decided mayamalavagowla for different reasons… We know how it is… just like a language, it is not that the rules come first, but the usage and the music…