necromorphs can't follow the player through ventilation when he went the room

I have played this game about 40 hours most of them i spent of studying the intensity director. I noticed that in most of cases necromorphs cant get to Isaac through vent, when he went another locations although each room in the game have vent. They just stand there and do nothing until the player returns to the room. In the original game necromorphs could follow the player through the ventilation all over the deck. PLS FIX THAT