I have a little better ideal now. Thank you for the help. But I still don't feel like i have a clear understanding on the way the spring sits in the strut. So when you have to take the spring off it needs to be compressed with a tool to take the tension out. so the new spring will need to be compressed via the same kind of tool to be put back on the strut. So on the top end there is some limit to how long the strut can go.. Correct? I mean if it didn't you wouldn't need to compress the spring to fit on the strut at all.... So if you had a spring that was say 2" longer even it wouldn't now give you 2 more inch lift... I have watched countless videos on changing springs on struts and the overall assembly looks to be the same length. I might have to go up to my shop as they are doing this to compare one with and one without to see the actual difference of the overall assembly.I think I understand what you're thinking, but it's not correct. The spring/shock is not compressed in some fixed area that limits it's length. In fact its the opposite, the spring stiffness and height determines how much static space there will be between the suspension arms.
The shock doesn't capture the spring in any way. It sits inside the spring and aids in how the spring moves up and down, but doesn't limit it in any way. The suspension the shock/spring are connected to have a lot of travel up and down. The taller springs means the suspension is extended farther and gives the higher ride height.
You are right in that a stiffer spring of the same length will have similar effect, but would hurt the ride. That's why a longer spring instead of a stiffer one is preferred to help maintain a smoother stock ride while offering a higher ride height.
That's why when people want to lower a car for cheap, they simply cut the springs or buy shorter springs. Adding a spacer to the spring or getting taller spring does the opposite.