Scheduling third party resources only when internal resources in territory are busy is not working

We have created a territory that has internal resources (Individual resource, Group resource) and Third party resource (Group resource). The goal is to assign task to internal resources first and then, if all resources are busy, to the third party group resource.

Scheduler rules have been set to Prefer Internal Resources.

But every time we schedule a task, even when individual resources are available, the SR and the task gets assigned to Third Party.

We are expecting that SR gets assigned to Internal Group and Task gets assigned to internal group / Employee Resource but SR is directly getting assigned to Third party and so does task