but my suspicion is that the A16 will give me 16 separate array elements

Why would you think that? Test it out.

#/usr/bin/perl
use strict;
use warnings;
use Data::Dumper;

my $line = "FooBarBaz";
my @array = unpack('A3A3A3',$line);
print Dumper \@array;
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Produces:

$VAR1 = [
          'Foo',
          'Bar',
          'Baz'
        ];
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So A16 will produce 1 element.

As to your signature: I would suggest reading something I wrote earlier.