Donnie Brasco, an associate, paid a percentage of his money he made to Lefty Rugierro, a soldier. He works directly for Lefty. I'm in the middle of his book and now Sonny Black, a capo, offers him to work directly for him, without first contact Lefty, his (former) mentor.

But Henry Hill, also an associate, paid a percentage to Paulie Vario, a capo. He works directly for him. Why didn't Hill have a soldier as mentor were he works for, like Donnie Brasco? Why did he worked directly for a capo?

When is an associate allowed to work for a capo (and not for a soldier)?