Using a look-ahead will allow for overlapping patterns. However, @+ contains the same values as corresponding elements of @- when look-aheads are used so sums are necessary.

$ perl -e '
> $str = q{CATINTHEHATWITHABATATINAAAT};
> $rex = qr{(?=([^A]A+T))};
> printf
>    qq{Found %s, length %d at offset %d to %d\n},
>    $1,
>    length $1,
>    $-[ 0 ],
>    $-[ 0 ] + length( $1 ) - 1
>    while $str =~ m{$rex}g;'
Found CAT, length 3 at offset 0 to 2
Found HAT, length 3 at offset 8 to 10
Found BAT, length 3 at offset 16 to 18
Found TAT, length 3 at offset 18 to 20
Found NAAAT, length 5 at offset 22 to 26
$
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I hope this is of interest.