"I'm so happy to see you!" is what my sim would love to say to the visitors... if he wasn't busy running after them.
So there's this thing, where visiting (or delivering) sim rings a doorbell and kind of walks away from the door (hopefully I'm not the only one to have it). Sometimes they would still stay on the porch, sometimes walk a little further and in case of my new apartment building - they will ride the elevator all the way to the main floor and walk outside (and so few times, actually). So greeting a visitor becomes an aggravating and time-sensitive issue. Here's what I would love to know - does anyone knows the rules of the "walk-away" and is there a way to nicely ask sim to stay close to the door?

I've noticed if I queue a Greet while they're near the door before they reach for the doorbell, they're more likely to stay there. But the timing's a little tricky and if the space in front of the door's limited, they'll wander afar anyway. They sometimes go back to the mailbox but sometimes they go around the side of the building.

@SIMposiast, I noticed that too, but it's so frustrating to just sit there, watch and wait for guest's perfect distance to the door. Which is why I'm wondering if maybe more experienced players know some guidelines to follow when building a house.

If you don't care about them actually going inside the house, you could try greeting them before they get to your door? I do this all the time since I hate sims coming inside my houses and hogging the bathrooms. 95% of my sims' visits take place on the sidewalk, haha. If you want them to come inside you can always walk back to the house, and then call them over, though depending on the size of the lot you then waste time just walking there and back.

It uses Generic Sims Call 0x02b ([prim 0x0001] Generic Sims Call (Is It Ok to Idle Here ).
A Generic Sims Call calls back to the Game's executable so it not something we have access to, generally sims are not permitted to idle on the threshold of a portal as well as probably a few other places so if moving away from the door places them near another door, a stairway or elevator then they'll have to move away from there until they find a clear space.

It's not a problem I've encountered but I guess we need to design our lots with enough room around the front door for them to be able to move away from the door without standing in the way anything else.

I rarely have a problem with it. Most of my sims homes are close to the street so it's just a few steps for my sim to reach a person at the mailbox. A few houses have a front porch but it is usually big enough that the visitor stays on it and doesn't go down the steps.

Visitor: "Try to catch me if I ring bell at first at front door and then at back door and then going to uncertain point. And if your greet drops out of command I will go home through your house out of front door."

Wow, so many of you engaged @butler-pate, I also used to hold an outside visits, there is something very efficient about that
@Chris Hatch, thank you, that is exactly the information I was looking for. So now I'll just have to do some remodeling...