I get the impression that you can only give the reference of the tied object and the key to the FATCH method (correct me if I'm wrong). If you give a tied array to your tied hash it will work as well. Here is my code that proves this (I hope it is useful)

use strict;
use warnings;
use Tie_hash ;
use Tie_array ;

  my %hash;
  my @arr ;
  tie %hash, 'Tie_hash' ;
  tie @arr,  'Tie_array' ;
  $hash{'key'} = \@arr ;
  print $hash{'key'}->[0] ;
  untie %hash;
  untie @arr ;

  package Tie_Array;

    use strict;
    use warnings;

    sub TIEARRAY {
       my $obj = [ "hi" ] ;
       return bless $obj, shift ;
    }

    sub FETCH {
      my ( $self, $key) = @_ ;
      return $self->[$key] ;
    }
    sub STORE {}
    sub DESTROY {}

   package Tie_hash;

    use strict;
    use warnings;

    sub TIEHASH {
      return bless {}, shift ;
    }

    sub FETCH {
      my ( $self, $key) = @_ ;
      return $self->{$key} ;
    }

    sub STORE {
      my ( $self, $key, $val ) = @_ ;
      $self->{$key} = $val ;
    }

    sub DESTROY {    }
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Cheers
LuCa