Thanks a lot ! Sadly there's still a small bug. Now the item renders at twice the Z elevation set. For example I made a small gif. I created two 3D Objects cube, that have a scale of 16. So, If I set a Z Elevation of 16 to one of the cubes, it should render at the height of the first cube. Yet it seems to render at twice that Z Elevation. The 3DObject blue selection square is located at the right position tho. I tried with different scales, but even with a scale of 1, the issue is still there, so it's not scale related. I don't know exactly where the problem is, but there's a x2 somewhere :p.
Good to notice it's only editor related, in game it renders at the correct Z Elevation.
We're almost there !