Yeah, balancing how much the reflections show the monsters and still make it see behind you was a weird balance.
The code for the safe is 4 numbers, which are all only seen as reflections using the phone. They can be a bit tricky to find without knowing they're there. There is a number inside each room that opens with a key, whether it be in the mirrored or regular version of the house.
Thanks for the feedback, I was hoping the numbers wouldn't be too hidden. I'll keep that in mind.