Victron Modbus Integration slave values greater than 248

I have managed to get my Multiplus and BMV connected to HA and set up a number of sensors and measurements. All is working very well and I am pleased with the results so far.

However, now I am trying to create additional sensors where the slave is not 100 i.e. not the system registers and they are all above 248 which is causing the sensors to show up as unavailable. How do I address these registers?

Did you get it to work? I am struggling to understand what my slave number is to start with. How do you know that?