Because persons in the rich and powerful class paid carried choyo (national tax) and fubutsu (collected goods as tax) to Kyoto, Ingu oshinke (imperial families and powerful nobles) became related to these rich and powerful persons to secure the fubutsu that constituted their income.
調庸・封物を富豪層が京進することにより、院宮王臣家（皇族・有力貴族）は富豪層と結びつき、自らの収入たる封物の確保を図った。