Ok I saw a great tip on You Tube about classics and the White dust bags.
Instead of putting the bag in facing forwards (facing the front of the dustbag where Cocos head is) but it in so the back of the bag faces the front and then tuck the chains in the pocket of the dustbag and then fold that back over so the chains are then sitting on the back of the bag and not on front of the bag so the bag wont get a lean forward. If that makes sense? I can take a photo later to show you if that helps?
I brought a preloved Jumbo and she did lean forward when sitting up but once I switched storing her "back to front" in the bag, she came good and I have never had an issue. It seems much better if the chains are in their pocked laying on the back of the bag.