I think the vacuum has to be symmetrical, like the inside of a perfectly round balloon. But you can put some marbles and some marshmellows in the balloon and bounce them around without altering the volume or changing the roundness of the shape of the vacuum. I think the shape has to be constant and unchanging except for it getting larger in diameter. The vacuum (pull) has to be the same at any and all theoretical points inside the shell for the mechanics of the universe to work properly and predictably. Just don't ask me to explain. I'm having difficulty completing the model. Thanks.
Thanks for the ping. Can you tell me what I’m trying to say here? Thanks.