In Ignition, don't set up a Modbus Address map. Just create OPC tags in the Designer that use the Modbus address syntax described in the user manual.
e.g. [DeviceName]HR1 or [DeviceName]1.HR1.
The most common problem with addressing is that Ignition will default to unit/slave id 0 and some devices/implementations will default to 1, and not respond to 0 at all.