The effect should be added to the item, that is highlighted/selected

When user creates a new 3D project and adds a new instance through the effect's context menu (Content Library -> Effects -> Add an instance), the effect is always created there, where it was first time drag-and-dropped.

It might be better, if the effect is created under an item, that is highlighted/selected, for example, a different model in the same project. If none is selected, the effect could be created in the center of the 3D view (under the scene)