Bookworm,
The size of the protected area at the end of the outbound leg is suficient to contain the aircraft allowing for any inadvertant difference between the ideal and actual position of the aircraft.
Even if the protected area was 50nm either side, you would still be required to follow the given outbound track as accurately as possible. Thus the actual size of the protected area should have no influence on how accurately you try to fly the procedure.
Regards,
DFC