There is full coverage of CAT evacuation issues in this excellent RAeS specialist paper:
www.aerosociety.com/emergency-evacuation-of-commercial-passenger-aeroplanes
I understand the 1.8m max height requirement originated in the US, which seems a bit arbitrary until you consider that 1.8m= 6ft, which makes it definitely arbitrary rather than science-based in my book. Whatever, it is still a long way to jump, especially if you are small or not in the first flush of youth. It is just like the view of (eg) a 3m or 10m diving board - from the ground/water looking up, jumping appears easy enough, whereas you get a very different perspective looking down from the board itself.