As θ increases, the normal force (FN) decreases.
Work Step by Step
Normal force is equal and opposite to the force of gravity on a flat plane like this. So when the force acting downwards increases, the force acting upwards (normal force) increases with it. Increasing θ increases the vertical component of the force, meaning that more force is pulling the box up. When more force is pulling the box up, less (normal) force is exerted on the box.