A stack that works is a stack whose chains never meet. That is the whole craft, and it comes down to three numbers.
Lengths
Leave at least five centimetres between chains. Forty, forty-five and fifty-five works; forty-two, forty-five and forty-eight does not, and will spend the evening knotting itself at the clasp.
Weights
The heaviest piece goes on the longest chain. It sounds backwards and it is the reason your shortest chain rides up: a heavy pendant on a short chain pulls the whole stack forward.
Metals
Mixing metals is fine and always was. What is not fine is mixing two yellows that are nearly the same — 18ct beside 14ct reads as a mistake, where 18ct beside white gold reads as a decision.
