This bit of the FTC6 manual…
…has the following footnotes:
*8 Valid only when operating in Room temp. control mode.
*10 Valid only when operating in Heating room temperature.
*15 When DIP SW5-2 is set to OFF, the function is active.
Where DIP SW5-2 is for “Advanced auto adaptation” and is on by default.
Unfortunately my system is in a tiny airing cupboard and reports the “room” to be 25 degrees all day, so room mode no use to me but maybe it’ll help someone else.