The number of elements only decreases, when the last element is delete()ed:

$ perl -wle 'my $a=[2,3,4]; delete($a->[1]); print scalar @$a'
3
$ perl -wle 'my $a=[2,3,4]; delete($a->[1]); print scalar @$a'
3
$ perl -wle 'my $a=[2,3,4]; delete($a->[2]); print scalar @$a'
2
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