Found the rules and you are, in fact, quite correct! My bad.
This tile moves as soon as you enter
it. Roll 2 dice and put it adjacent to a
connecting door on the appropriate floor.
(If there isn’t one, leave the tile where it
is.) If you roll the floor the Mystic Elevator
is on, you can move the tile to a different
connecting door on that floor. You can use
the elevator only once a turn.
Monsters and the traitor can both use the
Mystic Elevator to go wherever they wish
without rolling. However, the tile still
moves only once during each entire traitor/
monster set of turns, the first time either a
traitor or monster enters it. In other words,
if the traitor uses the Mystic Elevator
during his or her turn, then it will not work
if a monster enters it on its next turn. A
hero must roll for the destination floor each
turn he or she enters the Mystic Elevator,
or at the end of each entire turn that hero
spends on that tile without moving.
If one or more explorers are already in
the Mystic Elevator and another explorer
enters it and rolls a 0, all the explorers in
the elevator take the damage.
If an effect of another tile or card leads to
the Mystic Elevator (such as the Collapsed
Room or Secret Passage), the token placed
by that effect stays on the Mystic Elevator
tile even if it moves. "
Given that I completely misunderstood the rules and it IS a roll upon enter, then I'd actually think the blueprints would apply then. Huh.
Learn something new every day! I've been playing it wrong all along. XD