APM behaviour change v11.2 to 11.3

I'm not sure exactly what changed in 11.3HF5. Have a feeling it's related to routing domains but before we upgraded from 11.2 to 11.3HF5 I was able to have my APM front end virtual server in one vlan then access a portal resource on another vlan. This resource was just a basic http web server. I did NOT have to setup a virtual server to front end that back end web server. NOW APM will not access any back end resource that is not setup as a virtual server. Also, before in 11.2 the APM VS and the backend resource were not only in different vlans but different routing domains. It still worked. APM just sourced traffic from it's vlan self IP around through my firewall to the back end web server. Now it cannot access that back end web server. I honestly don't see it coming out of any interface. It's like it's getting lost in TMM somewhere. The only way I could get APM to work now is to setup the APM front end VS and the back end resource in the same routing domain AND setup the back end resource as a virtual server (to be used as a portal resource) Can you NOT access a back end web server via portal resource? Unless it's setup as a virtual on the LTM? Have been working with support but nobody can answer this question. TIA