How about this? You find the middle of the array, which will either be an integer or a half-value. Return the slice indexed from the integer portion of the midpoint through the integer portion of the midpoint + .5. If the midpoint is a half-value, those will be different (so you return the two values that straddle the middle); otherwise, they will be the same, and you return just one value.

sub Return_Middle {
  my $midpt = ($#_/2);
  @_[int($midpt) .. int($midpt + .5)];
}
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Update:
The text description in the OP suggests that the array is already sorted, so I didn't see the point of sorting it again. But my code could be a drop-in for drilldown instead of Return_Middle, or a sort step could be added to it:

sub Return_Middle {
  my $midpt = ($#_/2);
  (sort {$a <=> $b or $a cmp $b} @_)[int($midpt) .. int($midpt + .5)];
}
[download]