That is one way. The most common mounting is two fixed heel bushings, two gliding heel bushings, and no midfoot screws.Isn’t the soft SL the one with the two midfoot screws installed and 4 gliding heel bushings? I don’t think I’ve ever seen one set up that way on the rack,
The primary way to adjust flex is via the plastic "flex element" that sits in between the plate and the ski. The further forward, the softer the flex. It should already be fully forward from the factory. If you look at the side of the piston plate at the rear where it starts to taper upward, you should see only a small bit of plastic plate on top of the ski. Her 149cm should be the same. The Marker Tech manual only suggests moving the flex element rearward to stiffen up GS/SG/DH skis.