Red Dot Pistol Sight question
Several co-workers have purchased Glocks and Sig p320s with RMR and other slide mounted red dot optics. We are in the process of having pistol red dots approved as an optional item. I have been shooting iron sighted pistols for over 35 years and use them pretty well. I've tried a few of the red dot equipped pistols and found an issue that I'm hoping someone here can help me with.
Say I have a Glock 17 MOS with a Trijicon RMR2 and suppressor iron sights. The RMR2 and iron sights shoot point of aim/impact. My target is a 3x3 inch card at 15 yards. I purposely place the left edge of the front sight against the leftmost edge of the rear sight. This means the bullet will impact to the left and completely miss the card. While maintaining the above iron sight alignment/sight picture, I place the red dot on the center of the 3x3 card, I miss the target to the left every time, even though the red dot is in the center of the target.
What am I missing?