Restrict groups for Group picker custom field

Question

Hi all,
I've looked thoroughly through the community but I couldn't find an answer specific to JSM.
I'm currently trying to setup a Custom field Group picker.
I've defined the default group to be selected, but after configuring the field in the request, the field allows me to pick between all the Groups available in Jira, which I believe it's its usual behavior. 
My goal is to have only a specific set of groups to be picked from.
Is there a way around this? 
Can groups be restricted from Projects so these won't appear in this field?

Thanks

Mikael Sandberg · Answer

The custom field we are using is just a single select field. I then have an automation that sets that field based on the assignee.

Davide Cioranu · Answer

What type of custom field would it be? A group picker? 
I can't find any custom field which give me the option to link a value within it to an agent, unless that's not the work it is meant to be setup.

Mikael Sandberg · Answer

So my team is divided like that and what we use is a custom field called tier that is set based on the assignee. We also have an automation that auto-assign new requests based on a on-call schedule in Opsgenie.