Not quite. Unfortunately, the node size isn't that accurate (there are only 3 possible sizes I think). For now, the width is calculated by taking the size of the collider bounds of the decoupler and the parts two above the decoupler. This can however be the wrong result, for example if the part above the engine is a size adapter, with the shorter end at the bottom.
The height is calculated by the difference between the top and bottom stack node of the part above. At the moment, this doesn't take part offset into account.
That's the reason why there still is the possibility to set the size manually ; )
Not at the moment. What you want to do is to hard code a value for the size, so that decoupler x has a diameter and offset preset, rather than taking it from the collider size, right?
I might try to do something like that