Your trees do look very far apart. For that distance, I would expect the straps to be higher. The problem is getting them up the trees. You can use a stick to push the straps up the trunk and tighten the tail when they're up higher.
You can make yourself one of these hammock levels out of a plastic oatmeal or margarine top.
Hang it from your ridge line with a bread twistie tie. Judge the levelness of your ridge line with the top edge. Judge the 30 degree angles of the suspension with the side edges.
Pretty soon, you'll be able judge the angle with just your eye. Good luck!!