Several times in the books, it is mentioned that Harry put his cloak in his pockets (example taken from HBP, Chapter 26 "The Cave", p.391, American Edition) :
Harry pulled of his [Invisibility] cloak, stuffed it in his pocket, and followed.
Yet the Cloak is also big enough to hide Harry, Ron and Hermione at once (even if their feet are visible by the end of the series (DH, Chapter 32 "The Elder Wand", p.456, American Edition) ) :
"Harry, you get the Cloak on", said Hermione. "Never mind us -" But he threw it over all three of them; large though they were, he doubted anyone would see their disembodied feet through the dust
How is it possible for a Cloak to cover three people and yet being stuffed into a pocket (without an Extension Charm of course) ?
I'm looking for an in-universe canon explanation if possible.