the struggle comes from where your eyes are used to going to where the now should be.
let me elaborate.
for those of us who shot irons our whole lives, we were trained to have a hard focus on the front sight.
why?
because we had to focus there so we could then line up the front sight to the rear sight, properly align it, make sure the top of the front sight was even with the rears, it was centered in the rear notch (equal light on both sides) and then we could send the shot.
with irons, it's well, for a lack of a better word, the opposite.
the sighting system is simplified, there is no more having to 'align' anything but our eyes are trained to look at the thing closest to us.
You are now having to make that change in your eyes focal point and when starting off it is and can be a challenging venture.
Look at your target. Look at a very specific spot on your target and trust your index.
if you stay locked in on the target, trust that your dot will come to the right place.
Our eyes work like a camera, they struggle to focus on two things at once.
You should now be laser focused on the target and simply be aware of where the dot is.