Because the Inaba family was the most powerful domain in Kinai region (provinces surrounding Kyoto and Nara) having great influence over Saigoku (western part of Japan (especially Kyushu, but ranging as far east as Kinki)), Masakuni was also quickly promoted in the Edo bakufu (Japanese feudal government headed by a shogun) from the beginning.
稲葉家は西国に睨みを利かせる畿内随一の藩であることから、正邦も当初から江戸幕府内での昇進が早かった。