The harness will only fit comfortabely when it's tight, the hard shell conforms to your back, if it's loose it's pressure is in the wrong place. If you want to use it for wave riding use the rope spreader bar.
Agreed, Used a soft dakine that I would keep loose in order to slide a little and the ride engine is a different story. It's not suited to movement on your body. The lumbar curve shape of the shell and the rigid sides are just not comfy when the harness has room to wander. Feels great when its in place and appropriately tightened. Best harness I have owned so far.
The original premise of the RE rigid shell with slider is to offer a better option than loosening a soft shell to allow sliding. The rope slider is a great way to go, but depending on what your doing a pivot offers yet another option. Maintains accuracy at the bar yet eliminates the lever arm of a standard hook. Note the length. Takes a little time but you eventually realize having the bar position as close as possible to your core is not the best ergonomics and has you riding around with T rex arm posture. IMHO efforts to shorten the CL as much as possible are misguided. The sweet spot is the sweet spot and its not really in that close, especially for the dynamics of wave riding. This set up was done with the stock Ride Engine metal slider spreader bar by routing the line behind the stays in the spreader to the centre. Nice little bonus is the small loop at the base so you can run a standard chicken loop bar when needed. In that case the rest of the line with QR act as your leash and clips to the single line safety. Imparts a lot less wear on the poly covered CL compared to the friction of running along a full length slider.