That's a good point nothermark. I'm really not sure what angle it sags to when I'm in it. I'll get my wife to take a picture, and then I can measure it.
Right now, in light of the replies above, I'm going with the philosophy that so long as I'm off the ground and the ridge line is straight when I'm in, the saggier the better. I figure the more sag there is, the lower the strain on the trees will be.