If you draw a card with a spawn direction (say an Attic monster) but you haven't explored said location yet, does it spawn there anyway?
We have been playing it as the person who drew the card slides it facedown under the unexplored room. That way only they know what is there (they "heard" something) and have to explain it in game to other investigators.
Adds to the feel of the game.
You can post your variant as a rule variant, but this will most likely break the game balance in many scenarios.
If the location is in play, you still place the enemy there normally. (The enemy doesn't care whether you've been there or not). However, if the location is not in play (scenario 1 for example), then the enemy is discarded.