The cheater way to see what your angle is is to have a smart phone with a bubble level app that tells you. Or you could use the quick and dirty rule of thumb. When you make a right angel with your thumb and index finger the line between your finger tips is roughly 30*.
I could be wrong, really hard to judge distance in pictures, but it looks like your span is more in the neighborhood of 20 ft, 8-9ft for ridgeline and 5-6ft to each tree. If that is the case you'd want your straps to be over 7ft up the tree.
Keep messing with it and find that sweet spot, then it's nap time.