Non-standard flight levels and coordination
Last week, heading east via REDFA with London, I found myself in and out of a lightly icing stratocu layer at FL90. Being unpressurised I didn't want to go to FL110, so I requested, and was offered without comment, FL100 -- which would conventionally be a westbound level.
By contrast, I remember a similar occasion a couple of years ago heading south east via SASKI, asking for FL100 and being told that only FL90 or FL110 were available in that direction.
Does a non-semicircular flight level require special coordination with adjacent ACCs? Always, never, or does it depend on the adjacent FIR?