Here are some detailed video analyses of what the pros are doing. Look for the forehand comparisons.
I would describe all their forehands as having a high take back.
You should take videos, preferably high speed videos, of your strokes.
The book Technique Development for Stroke Production
, Elliott, is an excellent reference on the modern strokes. Available from the ITF for $20.
I'll offer a personal opinion/speculation as to why a high take back might
be important. The largest muscle attached to the arm is the lat (the muscle that works for a pull up). If the upper arm is out from the body then the lat can play more of a part in moving the arm. Does it go rapidly down a little to start the forward swing?
Three players to look at regarding an unusually high upper arm take back are Del Porto, Florian Mayer, and, recently, Gulbis.
Del Porto forehand-
Florian Mayer forehand-
Glubis 2013 forehand-