In order for the backpack to fit snugly on your back, you must adjust the carrying straps. These consist of the two shoulder straps and the chest strap. The length of the shoulder straps determines how far up or down the back the bag ends up, and the height of the chest strap. Adjust them so that the chest strap ends up over the lower part of the sternum. Below your chest muscles, but above the diaphragm. The chest strap affects the distribution of the weight of the sac. A short chest strap allows the chest and rib cage to carry a greater share of the weight, while a longer one shifts the pressure to the shoulders. How you want to distribute the weight is a matter of taste. If you carry the backpack for a long time, it can be nice to lighten or tighten the chest strap sometimes. The chest strap is attached with a rivet, and can be angled up or down to lie flat over the chest.
This is not nuclear physics, but clever nonetheless. The backpack's top lid is attached to the closure straps through loops and is held in place with two push buttons. If the usual packing space is not enough, you can easily unbutton and raise the lid a little to make room for an extra wool sweater for the trip.
The back rug fabric is saturated with beeswax and stearin. It keeps moisture out and creates a dirt-repellent surface, while providing stability to the fabric. The impregnation does not need to be redone. Just do not machine wash the bag, then the wax will melt away and the leather will be damaged. On the other hand, the leather keeps it´s goog prooerties being greased in from time to time. I use tip-top leather conditioner. There is probably other good lubrication as well, just watch out for scary teflon and other toxic debris.