Why? What information are you going to gain by looking at the lid halfway closed? The fully extended length is when the lid is fully open. The most compressed length is when the lid is closed. Both of those are depicted in my diagram. The points in between are irrelevant; at no point will the spring need to be anything other than between those two extremes.

If you move the mounting positions somewhere where the spring would bottom out, the lines depicting the spring turn red.

Set your desired fully-open angle. Set the length and stroke of the spring. Move the bottom mount point around. It'll give you all the information you need to know after that. The only vaguely hard part is entering how far away from the seam the lid end will mount.

The really hard part is figuring out where to place the spring so that it's strong enough to start lifting on its own at a useful point.