If that code is on the enemy, the enemy area mask must be the same as the player body layer, if the mask is the same as all the other objects, will detect them everytime (because other bodies may pass through the area).
If the area detecting bodies is on the player, the area mask need to be on the same as the layers it monitors for damaging objects (you can use different layers for each type of enemy or a single layer and filter in another way,).
Some ways to use layers:
layer 1: solid map
layer 2: player
layer 3: enemies
layer 4: general damage environment
layer 5: instakill
layer 6: immune bullets
Player: 1 (movement), 3, 4, 5, 6 (for damage)
Enemies: 1, 4 (player detect enemy already)
Could be more simple (all damage on one layer and use groups) or more complex depending on the design, you have 20 layers to play with.