Answer
The normal force is reduced when you pull.
Work Step by Step
By pulling at an angle above the horizontal, you exert an upward force that reduces the normal force on the crate, and also reduces the frictional force acting on the crate. This makes it easier to move at constant velocity.
If you instead pushed at the same angle below the horizontal, you would increase the normal force on the crate, and increase the frictional force acting on the crate.
