The case has small rubber feet on one side and the case is slightly dome shaped on the other, I think people will be able to place it correctly without an explicit instruction, plus there is only one “right way” to place it as it is already.
It would work for most people, wouldn't it? And the people putting their raspis into unusual scenarios for which the case was poorly suited could simply choose to not use that particular case. Encouraging thermal convection (ideally flowing over a proper finned passive heatsink) with a chimney design seems like a pretty good idea to me.