"As both strict and warnings operate for all the block regardless of where they are declared, I tend to use them to separate the head code from the actual mechanics of code."

This is not true, and you can verify it using:

$x = 1;
use strict;
$y = 2;
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Perl will complain about the use of symbol $y, but not $x because $x was used before strictures.

Both strict and warnings use lexical scope, which means their effect starts where they're imported, and continues until the end of the block they were imported into (that is, the closing curly brace "}") or if they weren't imported into a block, until the end of the file.