I'd be more than happy to take a look at their sheet. That is part of the issue is there is a lot of different theories on how spring rates should be calculated. I've always used the rule of determine the weight, divide that by the number of inches of compression you want (shaft showing minus shock length) by the weight to determine spring rate. Those rates are actually softer than what I came up with, however it is not out of line. Some theories in calculation say you need a certain amount of preload to adjust for ride height. I have found all of the theories get close, it is very hard to get it exact, there are too many variables, link geometry, center of gravity, shock valving, sway bars, all play a factor and all must work together. I genuinely believe either of the spring rates that either I and Accutune came up with will work, they are not that far off, they probably have a calculation for nitrogen fill that I do not have, with that, I bet mine and theirs are within ounces of each other.
If it were me and looking to get everything I could get out of a set of coilovers, they need to be installed and then carry the vehicle to someone to have them tune the spring rates and shock valving, coilovers are not a bolt on and it works out of the box. They are like building a race engine, they need to be tweaked to make the most power, no amount of canned, guessed at tuning is perfect. Just like tuning that race engine it takes, expertise, experience and being hands on to get the most out of it.
You can have the springs sitting loosely on the body, unbolted from the chassis, anything that that removes the preload from the chassis from the shocks, don't forget the nitrogen charge creates preload, the shocks do contribute some to unsprung weight, not a lot but do some.
