Previous post in the series: ACA Ceiling Grids: The Cell Component
One useful feature of Ceiling Grids is that you can anchor other AEC objects to the grid (just like any other AEC Grid). Once anchored, if you move the Ceiling Grid, the anchored object(s) will move with it, which makes small adjustments to ceiling grid locations much easier to do. You can find a number of Anchor tools in the out-of-the-box Stock Tool Catalog, in the Parametric Layout & Anchoring Tools category.
You could place the object at the desired location and use an Object anchor to tie the Grid, and if the Grid moves, the object would also move, but that would not prevent the object being accidentally moved, since the object can still be moved independently of the Grid.
Using a Node anchor provides the best result.
Depending upon how the Ceiling Grid was created, you may have to experiment with the sign applied to the offset values to get the object to the desired location. You may find it easier to select the object, right click and choose Node Anchor > Set Offset.
The Node Anchor will prevent the object from being accidentally moved a small amount. The object can be moved, but only from one node to another. If you copy the anchored object, the copies will be anchored to a node of that grid, also, making it easy to place additional copies within that ceiling.
Next post in the series: ACA Ceiling Grids: Mask Blocks