Sol Justacro

Hello,

I have been flying a Sol Justacro Harness lately, and am having a bit of trouble with it.
When flying it very upright it feels great but if I want to fly it a bit more reclined a crease appears in the back (maybe because of the weight of the second reserve behind shoulders), and the upper part of the backrest bends backwards, offering no more support. Needless to say it is very uncomfortable. Looks like it as something to do with lexan plate int the backrest which bends horizontaly while it should bend vertically (don't know if I am clear here;-).
Maybe I can fix it by adjusting straps but it is a long process as you can't change settings when loaded.
Anyone experienced something similar and have a tip about it?