Your code is much more complicated than it need to be.

It helps to write a function that prints the array in a defined number of columns:

sub print_in_n_cols {
    my ($count, @items) = @_;
    while (@items){
        for (1 .. $count){
            print "\t", shift @items;
            last unless @items;
        }
        print "\n";
    }
}
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Now you can call that, based on the number of dupes:

if (@dupes <= 10){
    print_in_n_cols(1, @dupes);
} elsif (@dupes <= 20){
    print_in_n_cols(2, @dupes);
} ...
[download]

Actually I don't why you want this behaviour, it feels more natural to me to always print in four columns - but of course that's your choice.