Do you still need flexible couplings 12in above and 24in below floors when risers are in service ducts, where there is no floor penetration or can they be omitted?

If you place a riser in a service duct, an open space without any floor penetrations in the entire building height, do you still need flexible couplings 12in above and 24in below each "floor" (NFPA 13 2019, 18.2.3.1) or do you omit them and place them 24in above and below the intermediate supports instead? (spaced at max. 7.6m according to 17.4.5.5)