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Fujitsu heat pump function setting help

We have new Fujitsu J-II Airstage heat pumps: indoor unit ARUH48TLAV, outdoor unit AOU48RLAVM. I'm trying to configure them, but the instructions are rather confusing. I'm using the J-11 Design & Technical Manual.

At the moment, my confusion is about control of external heaters (in our case a gas-fired boiler). I set indoor function 62 to 03, "Heater control using external temperature 1". This uses the heat pump alone above some outdoor temperature B, the heat pump with the external heater below B and above some other temperature A, and the external heater alone below A. I set these temperatures using outdoor functions 36 and 37, and enabled this type of control using outdoor function 35. All with this works fine.

However, in the description of this type of control (on page 08-38 of the above manual), there is additional discussion about control of the external heater based on the differential between actual room temperature and setpoint compared to the parameter Thon (indoor function 62). I have not been able to make sense of the description. Does it mean that the external heater will be on if BOTH the outdoor temperature is below B and the room temperature is far enough below the setpoint? Or that the external here will be on if EITHER outdoor temperature is low or the room temperature is far below the setpoint? I've try setting various values and as far as I can tell it pays attention to the outdoor temperature only. So maybe the manual is mistaken.

Anybody encounter these problems before? Thanks.
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