We have a short bit of passageway that drops almost 2" over 18" (I can
convert that to metric for you if you want). It's been like since the house
was built 60 years ago, I guess. It's not an issue, and nobody has fallen
there in the last 12 years since we have been in the house.

Based on that, I'd be tempted to put the whole of your 2cm drop over the
first foot or two as you enter the room and have the rest level. Otherwise,
you'll have problems with kitchen units and worktops which will never be
square to a sloping floor - I think the worktop needs to be horizontal.