Yeah, that thinner punty is a game changer for small stuff. I was fighting cracks on little florals for weeks. Switched to a 3mm and it just lets the marble cool more evenly, less stress. The thick one holds too much heat and shocks it. Total night and day difference on my success rate.
Read a forum post a while back where someone was saying the same thing. They broke down the science of it, how the thinner punty cools faster so it doesn't pull heat from the marble when you snap it off. Makes total sense now that I hear it explained.