Ok, here is some more hi-res pictures of the back to help determining the density (double-click for full screen).
http://img339.imageshack.us/g/dscf3571.jpg/
This is my 'out-of-bed' hair so scalp visible at the middle-low back is due to hair compression by pillows. The area covered with 24h old concealer is almost invisible here because it starts where the curvature of the head is placing it face upwards rather than backwards.

Also, two last pictures illustrate my question regarding template shape.

Top: should I go for straight lines or follow perimeter of good hair?

Temple flaps: have no idea how to cut them so any suggestions will be appreciated. My main concern is to make it blend with sides, particularly on the lower end. My hair in this region will be quite short.