No way will you be doing that by a hand held machine with a single phase compressor and especially at the height of a mur pignon.
I did a small section of my rear wall at 1.8m high & the dwarf walls of my car park & struggled to get a 12mm thickness, in most places it was a lot less, the brick wall had a gobetis cement first coat so I got away with it, the parpaing dwarf walls really needed 2cm, for your stone wall you will need that and more.
When I did an internal chimney breast on the 3rd floor I put it up by trowel but you cannot get 2cm in monocouche like that.
The only way is how the pros do it, with a pump using an Archimedes screw to take it to the projector gun which is powered by a TP trailer compressor. I say that after having tried everything over 8 years to avoid that investment, I can do small areas to the required thickness with my Sablon, my pal has a hopper gun with an Archimedes screw driven by a power drill, I modified it to use a much lighter and powerfull windy drill tapping off the same air source, again only good for small areas, the killer is the volume & weight of material needed & the speed in which it has to be applied.
We have scaffold and we got a quote a couple of years back and they wanted Eu.8k. Too much for us to spend on one wall.
That sounds like a lot of money but given the cost of the equipment, the material, the need for scaffolding, a minimum of 2 guys (better with 3) to mix & keep the rig running and to spray the material, that it sounds like you will need a gobetis coat before the monocouche (it is designed to adhere to new clean concrete blocks) maybe its not too wild.
The monocouche coat costs €35ttc/m2 around here based on a 3 or 4 elevation multi-day job. Areas like windows & doors you still pay the metrage price to cover the cost of masking, corner beads etc.