I just sent HB a long e-mail explaining this stuff as best I understand it.
The way I remember this, a knot generally reduces the strength of the line by 50%. And you do this for each knot. So if you start with 1600 strength and tie a knot to make a synch for the hammock end, then the strength is now 800. Then add another knot to tie the line to the straps and you are at about 400 strength... (please correct me if I am wrong).
Then take your hammock angle. 30% being optimal, that would mean that each line would support the same amount of weight, so a 200 pound man would put 200 pounds of force on each line. Again, correct me if I am wrong.
And this is just static weight. If there were some wind blowing and swaying, the weight is then calculated at weight*velocity^2, so a 200 pound guy could easily cause 400 pounds of force. And if the line gets wet in the rain it also loses some strength, which explains why both times I broke support lines on my old homemade hammock the lines were wet and the wind was blowing. That was prior to using dynaglide and/or amsteel.