from panasonic's installation manual http://panasonic.ae/en/manuals/C18KKS.pdf

top should have minimum 65mm
side should have minimum 50mm
this is because the air intake is at the top.  putting the ac too high obstrucs the intake and may lower the efficiency

an alternative is to install FCU (like hotel sytle), or dont put plaster ceiling

AC too near the ceiling won't be as efficient as it should be. You can mount it lower and use AC water drainage pump to drain AC condensation water throught the pipe.

AC water drainage pump

Hai looking at your site condition , you do not have sufficient space … bare in mind that from ceiling you need a gap of minimum 15cm … some even suggest optimum of 1ft gap for proper airflow …..you need this as it suck air on top and blows cold air inside your room …
Cheers mate
izwan
Www.archidstudio.com

https://www.mudah.my/1+5hp+YORK+AIRCOND+BB0030-99983922.htm

if you go for front intake type aircond, you can go as high as you want.
but sadly now is all top intake type

That's windfree... air outlet to prevent blowing cold air directly onto your.