Let’s look at this scenario below:
You add a decal to an object where the geometry stops at a certain point. Think of a split face on a wall, or a double door where there are 2 panel extrusions.
When you render the scene, a portion of the decal does not render. For example, if the decal is placed like this over a door it will render as follows:
The face the decal was applied to will render to the edge of the geometry. So in this example the decal renders to the edge of the first door panel extrusion.
For a situation like this with a component family, you could edit the family and use the Modify > Join Geometry between the 2 panel extrusions.
The decal will render as expected afterward as the face will be treated as 1 extrusion.
For another more complicated situation, if you apply a decal to a wall with split regions, you will notice the decal will not render.
Instead you can host the decal on another thin extrusion directly in front of the split face wall. Here’s a quick video below [no sound] on a similar situation:
If needed a transparent material can be applied to the thin extrusion if there is some overlap around the decal. Hope this helps!