Bosses like foremen often have assistants who act in their place when they can't be present. They are only there to do the routine jobs of their boss - not to set the tone of how the workplace will function like their boss would. Thus, like straw, they blow whichever way the wind (the real boss) blows. Like a straw man/boss they are just a copy of a real boss.

you hit him when his in midair

Synonyms for figurehead:cipher, front*, mouthpiece, nominal head, nonentity, nothing, puppet*, straw boss, straw person, titular head, token

From Wentworth & Flexner, Dictionary of American Slang, 1960 edition:
"'Origin of term: the boss attended to the grain going into the thresher; the second-man watched after the straw coming out and hence had little to do.' H. F. Barker. Colloq. since c1900; orig. hobo use."

it means: the last staw