La Sportiva SOLAR Owner's Manual page 6

4. Cuff adjustment system
You can tune to your personal forward lean preference by adjusting or removing
the wedge situated on the rear spoiler. To change the forward lean position,
insert the wedge in the lower slot as illustrated in the picture.
For a more upright boot, simple remove the wedge.
There are 3 adjustable lean positions.
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3. Fit instruction
It is recommended to unhook the front cable in order to simplify boot fitting.