Consistency of sight picture/alignment..

[YVK]

..at long distance: is it a function of visual acuity mostly, or something else is at play?

That was a short version of my question. The long one: I have been long frustrated with my handgun shooting at 25 yards and beyond. Seeing that I do better with easier triggers like 1911 or P7, I attributed my problems to usual suspects of trigger control and anticipation.
Recently I bought a spare slide for my Glock and had a reddot mounted on it. With that, I keep 90% of my shots on half (interestingly, upper half) of 3x5 card at 25 yards, as compared to 50-60% on entire card with irons. Obviously, the trigger control, anticipation etc aren't affected by the dot, so it must be sight picture/alignment.

Can anyone relate to this, and what do you do to correct it? I wear corrective glasses already.

[Failure2Stop]

A lot of people get bored with irons and lose sharp focus of the front sight during extended strings, causing the shooter to accept less than perfect sight focus, which is pretty important if you are shooting 3x5 cards at 25. Further, minor acceptable movement of the sight in relation to the target causes many to rush the last part of the trigger press; with an RDS the apparent wobble is minimized, which encourages full and proper shot process.

[FishingFool]

What irons are you using? Factory or aftermarket?

[YVK]

Heinie's, 0.125 wide front sight blade with 0.140 wide rear notch.

F2S, your explanation, as usual, makes a lot of sense. I do not have extended range sessions and in general, shoot long-distance early in my practice sessions as a part of "fundamentals refreshment". However, I can see how confidence in sight position over target with reddot may allow me to work trigger better.