the law of proximity in grammar

could you please lecture me a little bit on the law of proximity in grammar? pardon me if I get the spelling wrong.

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I presume that you are speaking of proximal concord, in which a verb may agree in number with a nearer noun rather than with its grammatical referent.

A group of boys are standing over there. – Although the sentence subject is singular (group), the verb is plural (are) because the concept ‘boys’ (a plural noun) is nearer it.

It is not a ‘law’ in the sense that you must obey it, but it does leave open the possibility of two natural formations:

A group of boys is/are standing over there
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On second thought, another possible ‘law of proximity’ is that modifiers (adverbs and adjectives) should be placed as near as possible to their referents in order to avoid confusion:

(X)The man gave me a sandwich who is sitting over there.
The man who is sitting over there gave me a sandwich
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The modifying clause (who is sitting over there) should be placed near its referent (man)-- just in case we might think it is a sitting sandwich (somewhat personified).
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sir, can I say about seventy to eighty percent of the students have or has improved?

can I also say a greater percentage of the students has improve?

70-80% of the students have…
70-80% of the water has…

‘Greater percentage’ is OK.

Sir, do i say: i was not one of those who was chasing her for tips
or i was not one of those who were chasing her for tips?