There is an issue with disk preparation step :
I set up a 20G qcow2 storage.
In partition manager menu i choose : 1 Assisted preparation.
Then i select disk to use : /dev/vda
Then if in the Partition Auto Menu i unselect boot (root?) and home and keep only swap

then i select 2GB for swap and i assume that 18 would be for both system and home.
Alas at some point installation stops due to not enough storage space.
Thinking it over.. I think the root partition is not presented because is assumed. So in that case root partition was created at 18G and not home ?