How do I set decimal values in 1D blend tree?

I have created a 1D blend tree. It is being used for a 3rd Person Controller.

The blend tree consists of 3 animations:

  1. aim pistol down to the floor
  2. aim pistol at middle of the screen (straight forward)
  3. aim pistol up in the sky

enter image description here

To determine the blend value (which animation should be played), I inspect the current mouse position and convert it a value between 0 (aim low) and 1 (aim high). The middle position would be 0.5. Here is my code:

float f = Input.mousePosition.y / Screen.height;  Debug.Log("Blendval " + f.ToString());// _animator.SetFloat("BlendVal", f); 

I tried to insert these decimal values in the blend tree like this:

enter image description here

However, this doesn’t work. Unity converts my "0.5" to 0. I don’t see why.

I can instead use integers like this:

enter image description here

Why doesn’t Unity allow me to use 0, 0.5 and 1? Why do I have to use "other" values like -1, 0 and 1?

Thank you!