The hurtzone of the NPCs is OK, but its "stomp" zone isn't.
Look at this image (1.4.5):

Now look at this one (1.3):

Both have the same hurtzone, but in the first image the player doesn't stomp on the goomba and gets damage.
The hitbox should be like this:
Green: "Stomp zone". The player can stomp the enemy at any part of this hitbox, it's not exclusively always from the top. (Height: 10px)
Pink: Hurt zone
- Spoiler

This is the level I used (note that if the block was 1 pixel below it would kill the player). The level is in 1.3 format:







