Why the mapping/coordinates/size have no effect on displacement modifier texture? I am coming from 3ds max and spent all night long trying to understand how the texture mapping work specially when use in the displacement modifier.

When i adjust the texture size in mapping only the image change and not the displacement.

I know there is another tab call image mapping where i can change the size of the texture but it is less convenient than the mapping tab where i can scale the texture in the negative.

Here a gif to explain it more precisely :
it looks to me that you are trying to modify the material texture not the modifier texture as they are not the same for blender. I am no blender internal expert though