You are 2 runs away from giving us the answer as to what the spoiler shim does in your Lange FR 120.
The spoiler shim in a Lange FR120 is velcro attached so that it takes all of 2 seconds to pull it off. That being said, screw the theory on what it does, and go skiing with it in and then take it out. Adjust the buckles and velcro strap according after removing the shim.
Then write the forum with your own assement on the benefits of the spoiler shim. This type of self guided discovery can be done the next time you go skiing. It will only cost you one run if you do not like it.
OK that is the easy part. Now let's look at the minutia of the spoiler shim......
It can either be for enhancing the fit or the performance of the boot. And that means both ways, either putting one in or taking one out.
For fitting it could:
Fill a void in the cuff volume by adding one
Give you more volume in the cuff by removing it.
Redistribute pressure from the achilles to the calf by adding or removing it.
Change the feel and fit on the shin of the boot.
And for performance:
It can be used as a gap filler to ensure that the calf and the shin are contacting the boot at the same time so there is no lose of control between being forward and being back on the boot.
It is an integral part of balancing your boot in terms of fore/aft. It can be added or removed to get a better match between the boots net angle between the boot board ramp and the shell spoilers forward lean angle.
It can also be used at varius heights to fine tune the above mentioned purpose. So it may not be just a question of in or out, but maybe up or down. With velcro attachment it opens up infinite ajustment possibilities.
The take away should be this. The spoiler shim is a great tool for adapting the boot for individual fit and performance needs. Diiscover for yourself whether there is a benefit in playing with it for you.
I see you are in Washington state, if you are in the Seattle area seek out Kelly Timmons for further guided discovery. Kelly was Langes WC serviceman for winning Athletes like Tommy Moe, and Picabo Street when they were winning. Or contact Tracy McCewan at Sturtevants Sports in Bellevue? she can steer you to the right bootfitter.