OK, so the minimum flow rate I measured at 2.57 l/m, so I would say that the manual is correct.
What happens with the burner and DHW temperature (at minimum flow) is this:
Burner starts, water increases from cold (~18C) to 48C.
Burner stops, water increases to 53C.
Burner starts, water drops to 48C.
Burner stops, water increases to 53C.
And cycles...
With a moderate flow, the burner stays on and the temperature is pretty stable at around 49C.
At full flow, the burner stays on and the temperature is stable at around 47C.
I would guess that the reason the burner activity/temperature seems inverted is because the boiler recognises the change in temperature internally before the tap (or rather my thermometer) can?