I tend to use the canon with a variant of the tripod scheme spoken of in "Ground Forces"
Planatary, mercs, and etceteras-directly serves a sub-organization and indirectly serves the Emperor
Army directly serves the Emperor through the sector dukes. pledged to Emperors service.
Marines-directly serves Emperor as strike force, and central reserve
also-Imperial Guard, directly serves Imperial family, as opposed to Emperor as Chief of government and head of state of the Imperium
Planatary, mercs, and etceteras-directly serves a sub-organization and indirectly serves the Emperor
Army directly serves the Emperor through the sector dukes. pledged to Emperors service.
Marines-directly serves Emperor as strike force, and central reserve
also-Imperial Guard, directly serves Imperial family, as opposed to Emperor as Chief of government and head of state of the Imperium