The temperature difference between the highest and lowest point in this room is is quite high, 20 degrees and the comfortable temperature (around 21 degrees is at 1.8m height). Because we spend most of our time in the lower regions under 1.5m, ie sitting or lying, this room will feel rather cold despite the heater working. We can see is as the entire bottom half room is in blue colour. To improve the comfort we need to force better circulation so the warm and cold air can mix better. We can do it by running the heater at higher fan speed or using the fan. Ceiling fans are most effective in winter because they push the warm air down to lower regions.
It is also important to be aware of temperature gradient when setting up the desired room temperature. The thermostat is usually inside the heater. Sometimes, with ducted heaters, it is in the control pad mounted on the wall. So we are setting the temperature not at the height we want it but at the height it is monitored/detected by the thermostat and to get it right we need to adjust the setting accordingly.