[SOLVED] Question about the requestor

Currently I have some users that are resources, other that are only contacts and some of them both.
When I add users that are both, to a project, they're automatically added as a resource and a contact of the project.
When I create a new ticket, we'd like to put as requestor only contacts but not resources, even if they're both.

Is this possible ?

Thank you in advance,
Regards