He mentioned that at some point they discovered that some rear fuselage strakes or "keels" worked well on a business jet, and to their surprise, did reduce drag in cruise, due to some modifications of the turbulent airflow on the rear portion of the fuselage.
These vanes are on all of the NG variants, to prevent tail oscillation due to the APU cone taper...
As noted, the MAX extended the taper at the APU, and removed the vanes...(same old story, reduced drag to add fuel efficiency,of course!)