So, you'd want to look at coverage path 4 - as in, "display coverage path 4". What that read out is telling you is that the primary coverage path for the station is 4, and the second one is blank and unused. Its a bit confusing. There's a feature where a set can have 2 coverage paths and use a feature code to toggle between them. My primary could be 38, which is right to voicemail, and my secondary could be 220 which rings my cell 3 times then goes to voicemail and I could have a feature code to toggle between them. That's ok - nobody uses that all that much. And its different than plain call forwarding. And different than ec500 that simultaneously rings your cell and set at the same time. There's about 1000 ways to redirect phone calls!
Anyhow, look at coverage path 4. Is it set to "yes" at "busy" and or "active" and not just "no answer"? That would explain why a second call to a station would cover to voicemail.
You can also use things like coverage answer groups - where a gang is in a group and calls to any one of the 5 that go unanswered will ring the rest of the gang for a few rings before voicemail too. It really all depends on what the stations are programmed to do, how calls get to them, what they share and how they forward.
You might just have a x ported station (exists in software only) where each of your pc support staff have a bridged appearance of that virtual phone's line they answer.
So, figure out a bit about that flow and you can figure out what the routing mechanisms are to get what you want.