"below" vs. "under"

I have read through questions about how "below", "under", "beneath", and "underneath" generally compare (both in stackexchange, and outside), but I don't feel that they gave a satisfactory answer for my specific question.

Compare the following sentences:

The marital status box is located below the street address box.

vs.

The marital status box is located under the street address box.

It feels to me that in this context, "below" means that the marital status box is located somewhere below the street address box, but not necessarily immediately under it, whereas "under" means that it's immediately under.

I am not a native English speaker.

I am interested to know if there is some rule that dictates such a difference between these two words.

If not, then I would like to know if a native speaker would also perceive it like me (despite it not being a "hard" rule), or if my perception is simply wrong.

While under and below are generally synonymous - and either example given would be acceptable and understood within the confines of a written form, say - the nuance in meaning is more apparent if you spoke those sentences aloud to someone who had no idea what you were talking about.

While "The marital status box is located below the street address box" would give a hint that you were referring to fields on a form, "The marital status box is located under the street address box" is more likely (than the first example) to conjure a mental image of a stack of actual, cardboard file boxes containing printed data.

In other words, under has a more solid, three-dimensional nuance than below - again, just a nuance. US