I have on a table 3 knifes. When I go in the front on the table, 2 of them react OK (they are behind me, invisible) but the third one is in front of me ! Do you know where I make a mistake ?
It sounds like it's a problem with baselines - however, without more details (seeing the room layout would help), it's hard to tell.
You can change baselines in the editor, or in script with the Object.Baseline property - just make sure it's higher than the player character could be standing.
EDIT: And please, try to use more descriptive titles in future.