I don't think HR is really that involved in the hiring process. They certainly aren't at my company. They'll read the job posting and make sure that there isn't anything illegal in it, but then that's it. It's up to the Engineering Managers to come up with a process, and make adjustments when there are roles to be filled.

This is the first time I've been involved in coming up with the process, but from what I've observed, it's a similar situation in other organizations.