Ok, so, I came across this during a weekend game. The answer may well be obvious, so I apologise if the solution is blindingly obvious and I'm just being obtuse... On the other hand, understanding the Valkyrie was never straight forward to begin with.
Scenario: my stormtroopers in their valkyrie arrive via outflanking and move 18 inches up to a Planetstrike bastion, pivots so the door is side-on to a building, and I declare that the stormtroopers are going to disembark on to the roof of the bastion. It's two inches from the door, so conforms to disembarking rules.
I'm then told that that will be a difficult/dangerous terrain test for the squad for attempting to land directly on the building.
Brief disagreement ensues, and for the sake of continued peace, I simply disembark at the base of the building and walk upstairs through the door next turn. Didn't matter to me either way - the scouts occupying the roof were mercilessly slaughtered regardless.
Still, it would be nice to have some clarification for future reference just the same. How do we handle disembarking from the Valkyrie directly on to the upper level of a building? Is it a difficult or dangerous terrain test? Is it clear terrain?