Consider the force and spring resistance at full compression, with the up/down travel balance. The spring you have to work with (or you choose) determines what you end up with.
Most near stock XJ's load the coil spring on front corners between 650 to 700 pounds, per corner at rest height. With all the weight on one front corner, crossed up headed down hill (or full tilt on a ramp), the load on the spring increases to between 1700 and 2100 pounds (between 2.6x and 3x the rest height corner weight).
You are going to end up with the ride height you get with the spring choice you select, and the up/down travel will be determined by tire clearance and bumpstop placement (what hits first when you fully load the corner). You can limit the up travel by using larger tires (that will hit the inner fender radius & coil tower bulge) or by lowering/raising the bumpstop contact point, but the coil force load on the corner will be the same.
You want the stop limit hit (tire or bump) to limit the compression travel, and then move the shock mounts to protect the shock at full compression.
If you want less compression travel to full hit, you install an air bump (or quality poly bump) to increase the spring + bump force at the final inches of travel, or you install a spring with a higher spring rate. The resistance provided by the spring needs to counter the corner load in fewer inches of remaining compression travel: 1200# in ~four inches (300#/inch) instead of a taller ride height with six inches of remaining compression (with a 200#/inch coil). A shorter 300#/in coil on an 12-inch travel shock leaves 4" up and 8" down, where a longer 200#/in coil provides 6" up and down, with the same force on the coil at ride height and at full compression stop. This is why spring selection is important (knowing what you have to begin with, and why all the guesstimate reports on rate we have make it near impossible to provide a quality answer to predict what you will end up with).
The need for better transient handling responce at taller ride height and the prerunnner demands for higher spring force at full hit has also driven a greater selection of coils with rates greater than 220#/in (something we did not have even two years ago, and needed). It's all in how you design the coil rate (spring wire diameter and coil turns) and the spring height (length of travel and length at ride height), tuned with spring mounts (spacers, ACOS, or other movement at the spring perches). We are fairly limited on what we can do with the spring perches (only move the top mount) so it limits the possible adjustment in ride height and travel to stop we can effectively tune.
The challenge of dialing in the spring rate and travel at full compression load highlight the advantage of coilovers in spring selection, where you are not compromising with only a limited selection of springs (rates, block lengths, and travel range lengths) and a limited choice of spring mount locations. The coilover options allow much more freedom to set the parameters.
I hope some of this makes sense? I have to eat and dump some new antibiotics down my throat to kill a two week old ear infection.
