Ansible Tower - isolated nodes.

I have Ansible Tower (AT) running witha single inventory imported from Satellite, inventory spans 3 sites. AT is configured with Tower in one site and isolated nodes in the remaining 2.
I want to be able to run a job against all the hosts across all the sites, the job currently fails for all the remote hosts as 'Failed to connect'
If I edit the template and only select one site in the instance groups the job runs fine.
Has anyone got Tower running across multiple sites/nodes and successfully running jobs spanning multi sites?

Thanks