The M1DBHR must be as close as possible to the M1 within the same enclosure. You can then connect the M1DBH in parallel with the M1DBHR making sure to remove the JP3 jumper on the M1.
J1 and J2 are in parallel with each other and are the same connection point as the RS485 Terminals +VKP, Data A, Data and NEG. J1 and J2 are generally used as temporary connection points for example bench testing. If you connect the M1DBH to J1 and another Bus Device to J2 this would be the same as Two Home Run Connections.