For the example configuration you show, the indentation would show as the following:

%indentation = (
                '0' => 1,
                '2' => 3,
                '4' => 2,
);
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Because I was potentially looking at multiple indentation levels, I believe I did something like the following to get the common indentation width:

# Yes, sometimes I write code in ways to make sure _I_ 
# remember what I was doing when I come back to it later.
sub gcf {
    my ( $i, $j ) = sort { $b <=> $a} @_;
    return( abs( $j ) ) if ( $i == 0 );
    return( abs( $i ) ) if ( $j == 0 );
    return( abs( gcf( $j, $i % $j ) );
}

my $common_indent_factor = 1;
my @data = sort { $b <=> $a } keys %indentation;
while ( scalar @data ) {
    my $f_1    = shift @data;
    my $f_2    = shift @data;
    my $f_temp = $common_indentation_factor = gcf( $f_1, $f_2 );
    push @data, $f_temp;
}
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This resulted in a common indentation factor of 2, which agrees with the observed.