Displace modifier - undesired artifacts in texture I'm creating a model that I want to later print in 3D. I am using a Displace modifier after a Multiresolution modifier to add a patern to some faces (using a vèrtex group plus displace on the Y axis to ensure that only the desired areas are displaced). 



However, when it is rendered, in the lower face that appears as selected in the UV map shown above, two undesired effects appear:


an horitzontal noise, that I think it might be the full texture that is rotated 90 degrees and compressed to cover the whole face.
some light displacement outside the vertex group, as you can see in a face in the back part of the model




I have recreated the materials and textures and ensured that there's only one UV map. I've also removed the displacement map and applied the texture as a verification, and in this case the object is properly textured, as you can see below:



... aaand, just before pressing the post button, it occurred to me that the multiresolution  could be causing a distortion due to the shared edge at 45°. I applied the modifier and inspected the generated faces. Indeed the generated subdivisions distorted the UV mapping, and also the vèrtex group spreaded towards the backward faces, creating the undesired displacement. So I modified the faces to ensure that all the edges are parallel. The displacement has improved a lot, but still there's an light, horitzontal undesired artifact...



I'm afraid I'm running out of ideas. Does anyone have some idea of what might be happening? Thanks!

---------------- ANSWER ------------------
I've marked the response below as an answer. I wanted however to summarise the things I've done to fix my problem:


I modified the mesh to have a more square faces. When I first improved the appearance of the displacement, I just removed the oblique edge and created a square at the righ-low corner. But was not enough to get rid of the artifacts shown in the screenshot. However, after seeing the answer below, I added some edge loops (3 to be precise) and then the displacement worked well.
I then applied the multiresolution modifier, and corrected the vèrtex group to which the displacement is applied, and got rid of the displacement noise in the back faces.
For displacement to work well all the faces should be equal size squares.