"I would not hesitate to evacuate if I knew the fire was above me, but below, well I might think it better to stay put, but might have a go anyway until I was forced to retreat back."
You have it the wrong way around. It would be better for the fire to be above you. Heat rises and if the fire is below you, it may be affecting the structure of the building. So if the fire is above you, it's best to let those above you evacuate. If the fire is below you, it's best to evacuate ASAP in my personal opinion.