Why does the bottom third of my BPH Bathroom Panel Heater feel cooler to the touch than the top section?

The BPH Bathroom Panel Heater has two elements inside it. A Radiant element and a convector element:

The radiant element is behind the metal front casing of the chassis shown in purple below.
The convector element position is to the rear of the chassis positioned in the grey text/arrow area:

Cool air enters the bottom of the heater and passes across the convector elements, rising in the process. That heated air then heats the upper two thirds of the panel metalwork as it passes upwards. The radiant element also heats the top section.

This is normal and by design, there is not a fault with the product.

Applicable Models:

BPH100M, BPH100G