well there are number of things that play into the science of it. FWD , RWD, AWD, . They all are sprung according to the weight bias front to rear and the shock valving , if the company building the setup is good and not just making off the shelf crap. The idea is a FWD is sprung stiffer in front vs rear because there is more weight in the front and the car is being driven up their as well so you a TQ and HP aspect . Plus the rear end is basically lighter and being dragged around.
Now RWD and AWD tend to still have a heavier front end than rear but more weight in the rear compared to FWD. Plus the RWD car is being driven from the rear.
Road conditions can play into this as well as well as getting the proper front to rear suspension freq for the best handling . Thats some of the more advanced stuff though.
Hence you usually see a somewhat softer rate in front vs rear. AWD cars and in our case with ours can be sprung towards a RWD setup because or weight distribution is closer to that of a RWD even though we are driving our front wheels as well as our rears. Which leads in an off road situation to some spring manufactures going 50-50 . It’s interesting that Ohlins has gone 50-50 on our cars like they did on the GR Yaris and a few other suspension manufacturers did for the GRY as well.
Factory our spring rates are 5k front 6k rear and the Morizo is 5.5 front 8 rear. Annex picked 6 front and 9 rear , Ohlins went 9 front 9 rear I believe . Now some of this can also be worked out with the valving of the damper as it plays a role. No pun intended. This is interesting because it’s exactly the way Ohlins made their setup for the GR Yaris and several other GR Yaris suspension manufactures did as well the some did do the softer front stiffer rear .
Like others have said a lot of these manufactures literally take the concepts they use on other vehicles and make adaptions to our vehicles to make them work on our cars. Not always are these ideal.
Sometimes buyers choose different spring rates to tune to their application aka a certain track or street use or drag or off road etc. The better manufactures actually spend time doing shock dyno testing and making sure the valving is specific for our vehicles and spring them accordingly . One usually pays more for that kind of setup.
So given that your stock front end is already at 5k and the Morizo is 5.5 one could say he choose 5.5 because and I am guessing on this that he felt 5.5 being picked for the Morizo was more suited to what his use was going to be.
So in picking a setup look for the manufacturer that goes the extra mile for our platform and designs specifically for it rather than generically.
In that sense it does seem like Annex is taking the time to do it right but of course one could say that about others as well. Until people buy the particular brand and run them we do not know completely without feedback.