As important it is to zero our sights properly, the distance at which we do it makes little real-world difference. Not if you are using iron sights, at least. If you are using optics, it is a different story.
9mm bullets run pretty flat at normal handgun distances. Not because they are so impressively fast, but because handgun distances are so embarrassingly short. Gravity has less time to do her thing on a handgun bullet over typical handgun distances (25m max) than on a rifle bullet at typical rifle distances (100m minimum).
With iron sights, the bullet crosses the line of sight not once, but twice. The typical 25m zero is, in fact, on the second zero point.
The bullet exits the muzzle about 15mm below the front sight, crosses the line of sight at 12 - 15m, crests and drops back past the line of fire at your 25m zero point. It kind of hugs the line of sight, never deviating from it by more than a bullet diameter anywhere between 5m and 30m. That is flat in anybody's books. Whether you zero your sights at 10m or 25m, does not make any practical difference.
I won't blame you if you want to check this for yourself. The ballistic table below is a good start.
You will also see in the table that there is not much of a difference between 124gr and 147gr bullets. That is not to say that ammunition has no influence - some bullets just leave the barrel differently. That is why sights can be adjusted or changed. The downward curve of the bullet path is just not as dominating as we expect it to be.
So why do we shoot low at longer ranges?
Because we shoot low at closer ranges.
It is just disguised by that impressive looking ragged hole. But that ragged hole at 7m is often just a little bit low and, after increasing almost fourfold to 25m, it is significantly low.
Optic sights are an altogether different story. For two reasons.
Firstly, the muzzle is significantly further below the sighting pane, so the barrel is angled more upwards and, for the same reason you aim higher when you want to throw a rock further, the bullet travels significantly further before cresting. This pushes the first zero point beyond 25m, and with that, the crest. And the crest is what gave us that nice, line-of-sight hugging bullet path that we saw when we looked at the iron sight ballistics.
So zeroing your optic equipped pistol at 25m will have the bullets start well below the line of sight and stay below it, all the way to 25m where it crosses it for the first time. All rounds fired at shorter ranges will impact a little bit low. At medium distances, it will be negligible, but at close range sight-over-bore becomes something to be reckoned with.
You may also choose a zero distance closer than 25m. That will have the bullet crossing the line of sight at the zero distance, continuing to rise to 25m and beyond. Since you will be splitting the difference above and below the line of sight, the "point-blank" range - the distances over which you don't need to worry about corrections - will be wider. But when you do need to make corrections, it will be more complex. Sometimes over and sometimes under. And changing more with changes in distance.
Another reason why you may prefer a 25m zero is that, at the longer the distance, your optic may have a smaller parallax error. Despite what it says on the box, any optic is only parallax free at the design difference, and that is usually further than 25m. It can be overcome, but it is one less thing to worry about when trying to make tight groupings.
At the end of the day, there are practical considerations to consider too.
You need to be able to look at your grouping and visualise the centre. Too close, and deviations aren't shown up well enough. Too far, and you have to resort to counting blocks to make sense of your grouping.
So, keeping in mind that iron-sights are not very sensitive to zeroing distance, that is my recommendation:
Sight adjustments steps are another big - probably bigger - consideration. It is not as fine as we tend to think. Swapping an iron sight can typically make a difference of 25-40mm at an average distance, while adjustable sights change a more useable 5mm per click. Compare that to the 4mm that the bullet drops towards the outer limits of our abilities, and you will see that we can't really fine-tune for distance. (Now is a good time to check that ballistic chart again.)
Whether I shoot iron sights or optics, I practice accuracy at the longest distance at which I can see my hits clearly ... that distance seems to be getting shorter these days, though. To get the best possible feedback when practising accuracy, I zero at about the same distance.
I do understand that a couple of metres this way or that does not make a big difference, though.
Whenever I advise people on sights, I just assume that the bullet is running perfectly straight and ignore the zeroing distance. That is not to say that ammunition can't make a noteworthy difference and that there is no value in selecting the right sights. But overestimating the significance of the ballistic curve leads us down ways that spoils our ability to get things right.
Like thinking that we're shooting low because of bullet drop. First, we shoot very carefully over a rest, then we start adjusting sights.