Didn't Ricca use Nitti technically as a "front boss" way back then? Or did Nitti know people were meeting behind his back with Ricca and just couldn't do nothing about it?
What about later on with Ricca and Accardo when Giancana was boss? They say big picture-wise nothing would get done without their approval so you can't just count them as senior "advisors"

-I shot him a coupla' times.
-What's a couple?
-Hmm, more than a couple... Really I don't know the exact amount, maybe I shot him 10 times, 12 times?
-Maybe fifteen?
-Hmm, it could've been fifteen...

-Anthony "Gaspipe" Casso