After the stretch is out, there has been no need to repeat the tighten, occupy/stretch, re-tighten. The first setup does it and the sag angle doesn't change. I have affirmed this by setting up, measuring, having the hammock occupied and measuring, getting out and measuring again, occupying and measuring. No change in either the occupied or unoccupied the sag angles, which consistently differ by about 2 to 3 degrees. This obviously requires 2 people to occupy and measure, but other than that it's dead simple so long as one person can read the scale on the inclinometer and that also is dead simple.
Differ with different suspension ropes? Well if you look at the type of ropes I used they are all dyneema. The Spyderline is a dyneema core with a polyester sheath. The others, Lash-it, Amsteel and AS-78 and all coated with a Samson proprietary coating. The results were consistent across all of them.
I was using my Carabiner Hitch method which I detailed in these posts. The method has a mechanical advantage built in. Usually I just used the basic 3:1 advantage. I didn't find going any higher necessary for me. I liked the Carabiner Hitch better than a Trucker's Hitch since the abrasion on the rope was negligible and the loss in mechanical advantage due to friction is also almost negligible. The friction, and hence abrasion, is the biggest disadvantage of the Trucker's Hitch.
With my version of the SLS method I use now, I choose the desired sag angle before hanging the suspension and set the sag angle when I tie the final end bowline knot. On spans over 18' I have found that using a 22 or 20 degree sag angle is almost mandatory for me. With spans of 14' to 16', I like a 24 degree sag angle and about 28 degrees below 14'. I don't use anything below a 28 degree sag angle since the sag angle my Bridge suspension triangle makes with the ridge line is almost exactly 30 degrees and hence with a 30 degree sag angle at the tree, the ridge line is hanging limp and pretty useless for accessories.