Making an inclined bed

I am interested to what length of the bed do you increase 6 inches . I watched the video in which Andrew says that the bigger beds can be risen to over 6 inches but not mentioned how much bigger beds in inches or better in centimeters . For example my bed is 2oo cm in lenght. Yet I'm interested what is the minimal incline or raise of the the bed of that lenght on which appears gravity circulation .

Just getting rid of my memory foam mattress today. Not very good imo Took me a long time to realise these mattresses are inferior to traditional sprung mattresses. We chose a natural filled mattress, padded with lambs wool. Very heavy to lift. Sleeping on it first night tonight

Hi,
Your 2 metre long bed should be ok raised 15cm To calculate the 5 degree angle use this right angle calculator.
www.cleavebooks.co.uk/scol/calrtri.htm

We have used the non-slip fabric that is for preventing rugs and door mats from sliding on the floor. This placed between the mattress and the bed eliminates mattress movement.