Once you have the stable stance and a solid grip, why are you still unable to remain consistent in your shots? What is keeping your grouping from improving beyond 4" at any distance? Your front site is locked in, or your red dot is on point, you still cannot hit that central site repeatedly and in a manner to know it will always be where you want it when you pull that trigger.
What is your finger doing? What is your finger NOT doing? The illustration on the right is a partial rendition of the issues you can create when you are not focused on what that trigger finger is accomplishing. Having too much or too little contact with the trigger and inside the guard can cause the muzzle to track side to side on action.
Give this exercise a try, hold your trigger finger out and try to grasp any object with the remainder of your hand without moving that trigger finger. YOU CAN'T. Now, try the same exercise, but keep your fingers on your hand straight, like you are clamping onto the object and not grabbing it. Voila! No index finger movement. How does that translate to your firearm?
What this will do to your aim is very similar to over or under placing your finger pad on the trigger mechanism. If you are grabbing the trigger you will pull the firearm toward your support hand on firing and you will shoot to the side. This is why we "squeeze" the trigger and not push it, pull it or other sharp action.
The flip side of the trigger squeeze is following through to the reset point of the trigger. When you "slap" the trigger and release this seemingly small forceful action creates a nearly 10 fold or more reaction down the firearm at the muzzle, putting you off target. Those of you who are meditative and mindful will recognize this pattern I propose, "squeeze 1-2-3-4, fire release 1-2-3-4". Very similar to "breathe in 1-2-3-4, breathe out 1-2-3-4". This slow deliberate movement will be amazing to behold in how it shapes your accuracy in not just subsequent shots, but the initial fire as well. Try this as a drill, you will end up with a single hole and several bullets down range having hit that same spot, dead on.
Where is your reset point? Why does this matter? If you release your trigger all together you must travel that much further for the next shot and move that much more. This reduction in movement can translate not to improved efficiency of firing multiple shots, but also helps to maintain that grip and control. The less you maneuver your hand/grip/finger, the less your muzzle has a chance to "dance" away from your intended point of impact.