is
A vertical CRS wkid is gravity-related unless it falls in the Esri block defining ellipsoidal height per datum (115700 = WGS_1984, 115702 = NAD_1983, …). Every EPSG vertical CRS is gravity-related (3855 = EGM2008, 5703 = NAVD88, 5714 = MSL, 5773 = EGM96), as is the Esri 1057xx block (105700 = WGS_1984_Geoid).