Multicast troubleshooting

This diagram shows an outline of my network. Each router is a Juniper SRX240 running in flow mode. The red lines are layer 3 OSPF (/30) links, the black lines are access ports to video encoders or decoders.

I have a problem where the data from video Encoder 239.0.0.18 is being doubled, i.e. if I set the bitrate to be 10Mb/s then I get 20Mb/s going down the line to the Main Office router. If I change the IP address for the encoder to send video to 239.0.0.180 (an address I know has no decoder setup for it) then I still get the 10Mb/s going down the line to the Main Office.

The encoders setup at the 239.0.0.3 - 239.0.0.10 are working fine (i.e. data isn't duplicated). I think this may be because all routers have the following config

pim { rp { static { address 172.31.255.102; } } interface all { mode sparse; version 2; } } 

Should I add the router in the "Remote Office 2" to the static RP on all routers? If so, is there a way of doing this dynamically so I don't have to update all the routers when a new video encoder is added to the network?

Thanks.