Why is my ac/heat ductwork so dang sloppy?

[Tumbleweed1C4]

I repaired my flapper, bought and installed a vac canister, installed all new ductwork, and a new s-duct, and almost finished putting everything all together (with a new refurbished tach cluster ).
But I am not sure if I am missing something because the s-duct to floor vent/defrost box connection is looser than a goose. In fact, the whole thing is sloppy. The flapper box connection to the firewall box is screwed together, but not confidence inspiring tight. The s-duct is screwed on there, and then the floor/defrost box, and I feel as if I am relying on the bolt that goes through the firewall to hold the floor/defrost box to hold everything together, and it does a very poor job of it. I am starting to understand why the PO had a load of duct tape around everything. Not what I was hoping for. Here is a picture of the s-duct connection and everything together. It looks like it doesn't go in far enough to screw together as I can see the holes in the metal of the floor vent box and it is bottomed out. I flipped the s-duct around to make sure I had it on the right way and this ended up like it made more sense, but I could be wrong. What am I missing?