As an eye doctor, I see many patients (over 40) with this issue. I usually give them 2 prescriptions. For red dot sights we use the full distance Rx because, as the previous poster correctly noted, the red dot is superimposed on the target. For iron sights, I use a modified Rx. Not quite distance, but not quite near. I have developed a Rx that will keep the front sight clear as well as the target. I also have shooters bring in their particular pistols, as the barrel length make a big difference on the Rx.
Hope this helps.
Stewart