An interesting post Tony.
Our Tom cat has always been confident. He shows no fear of other cats or even large dogs. He has no interest in cardboard boxes at all.
By contrast our Queen cat has always been nervous and timid. She descends on any box/suitcase that is left around and finds her way inside. She purrticularly likes half packed suitcases. She (we?) is lucky she hasn't ended up in Kef a couple of times.
This behaviour seems to confirm what the experts think.