After several troops, I have tried an addition to the backpack...
At the longer troops, I was getting sore shoulders from 'popping' my shoulders forward to prevent the backpack sliding down my arms or taking the armour bells off.. I therefore decided to add a black webbing chest strap to the backpack straps. Mine came from a premade backpack straps spares kit which I bought from a camping store (UK Millets), so there was not even any cutting or messing around!
The left one attaches behind the pouches and the right one, behind the pauldron, so neither end is visible. The strap fits easily into the void behind the chest armour and cannot be seen at all.
I cant believe how comfortable and simple it is, and no more aching shoulders, and no slipping at all, the backpack is very secure and doesnt move now, a recommended upgrade chaps.
Nick