I think you’re looking at this problem from a very wrong point of view. Every perspective is correct, as long as you follow the rules like all parallel (in 3D) lines vanish in the same vanishing point and all lines on one plane vanish into vanishing points on the same line (horizon). Also no perspective is correct because people have peripheral vision…
In the layman terms, the perceived “correctness” of the vanishing point distance depends on the height of the painting you’re going to make (height, because I think the height is more limited in human vision? So if you make the height too big (= vanishing points too close to each other), humans will notice they see more than they expect to see?). As @Deif_Lou said, you can be making comic, which makes the height of the painting smaller, and thus smaller distance desirable. Another thing is that you don’t always have to show whole vision as a human is capable of; sometimes you want to just show a “zoom in” of a scene, which would result in a higher distance between vanishing points (take any perspective drawing, then crop it 1/3 from every side. It’s still looking correct, right? While the vanishing points are further away in relation to the canvas height). Krita restraining distance between the vanishing point to a specific number even depending on the height of the canvas would be limiting.
I think it would be a much better idea that for those who don’t have yet the intuition needed for choosing the distance between the vanishing points (which comes with experience) that the chosen perspective would kind of show whether it’s roughly correct or not, than restricting the vanishing point placement. I did find that with the new 2pp assistant, it’s easier to see with the grid, also there are always those two points that are somewhat stably staying on the line of the “center of vision”. For 2 point perspective, I can easily say that if you keep both of those points outside of the canvas, the result should be pleasant enough for the eye. For 3 point perspective it’s more complicated since you can have one of those points visible; but then the horizon is either very low or very high, so the other will for sure be hidden. But there is no easy rule to stop yet. Maybe with dedicated 3pp assistant there will be a solution for that, too. (Though I’d like to just make 2pp and 3pp in one assistant, but we’ll see. I don’t have any concrete plans yet).
You are welcome to suggest changes to the current assistant (including the new 2pp one) but here I’m not sure what change you even suggest, and if it’s limiting the movement of VPs, then I disagree. I could understand a request for a warning in Tool Options, for example - for 2pp it could consider whole canvas, and for hopefully future localized 2pp (in a rectangle) it could use that rectangle to check if it’s ok - but I’m not sure, I mean, that would be a bit rude of Krita. It’s as if Krita were to check the painting and display a warning “Your colors are too saturated, tone them down” because many beginner artists use too saturated colors which results in an ugly painting. But what if the artist did intent to use them? I’m not sure if Krita should intervene and overeagerly try to correct the artist in case when it’s not obvious that the user is making an involuntary mistake.