All hammocks do not use the same sag angle/ratio and the differences change how high you want to attach the straps.

My rule of thumb for the hammocks I use is shoulder height at 4 paces (12 feet) separation, head high at 5 paces (15 feet), and as high as I can reach at 6 paces (18 feet)... then I make adjustments as required.

Because of how my body mass is distributed, I need the foot end higher to keep my body centered in the hammock so I either attach the foot end higher than the head end OR I use more suspension line on the head end side of the hammock.

The center of your body mass wants to slide to the low point of the hammock PLUS suspension. For me, the center of my body mass is not the geometric center of my body-- it is shifted towards my upper body. If I did not make adjustments for this I would tend to slide towards the foot end of my hammock.

Another thing I have found is that when hanging above ground that is sloped from my head to my feet is that it is easier for me to work with that slope rather than fight against it. In other words, I have better luck setting up with my head on the low side of that slope than the high side... for some reason I get fooled judging the amount of slope when trying to hang it in the other direction and almost always end up sliding to the foot end.