My first idea was to pass in the width/height:

my $g = Games::Grid->new(
  border => 4,
  width => sub { $_[0]/4 },
  height => sub { $_[0] },
  fill => '=',
);

{
  my $W = $self->{terminal}->{_co};
  my $H = $self->{terminal}->{_li};

  $self->terminal->{WIDTH}  = $config{width}->($W);
  $self->terminal->{HEIGHT} = $config{height}->($H);

}
[download]

I suspect that may not be flexible enough to meet your needs, though...

How about using package variables for $W and $H, instead of lexical variables?

my $g = Games::Grid->new(
  border => 4,
  width => sub { $terminal::W/4 },
  height => sub { $terminal::H },
  fill => '=',
);

{
  $terminal::W = $self->{terminal}->{_co};
  $terminal::H = $self->{terminal}->{_li};

  $self->terminal->{WIDTH}  = $config{width}->();
  $self->terminal->{HEIGHT} = $config{height}->();

}
[download]