When using the Trijicon HD`s on the XDS you should use a combat sight picture. Put the front dot center in the cut out of the rear sight.....this will line up all three dots. Put the center of the front dot on what you want to hit. To make a head shot put the front dot covering the nose to hit the nose. With a combat sight picture your front sight will cover the center of the target and you should try to keep both eyes open. Let the front sight dot float in space in front of you. This is very similar and you should use the same technique when shooting a red dot on a rifle.
This target represents the XDS being shot with factory sights and Winchester white box 230gr RN. My pistol shot to the left constantly at 10 ft, this is not an error on the shooters part since the shot grouping was always tight and always to the left. After adjusting the rear sight slightly to the left, the impacts were centered. Using a 6' Oclock sight picture I was shooting low. When using a combat sight picture I was on target.