It can actually be done correctly, like e.g. safari does it in the top-urlbar mode.
- When a user scrolls content-up in any way, the header collapses immediately (or you may just hide it).
- When a user scrolls content-down by pulling, without "a kick", then it stays collapsed.
- When a user "kick"-scrolls content-down, i.e. scrolls carelessly, in a way that a when finger lifts, scroll still has inertia -- then it gets shown again. Maybe with a short activation distance or inertia level to prevent ghost kicks.
As a result, adjusting text by pulling (including repeatedly) won't flap anything, and if a user kick-scrolls, then they can access the header, if it has any function to it. It sort of separates content-down scroll into two different gestures, which you just learn and use appropriately.
But instead most sites implement the most clinical behavior as described in the comment above. If a site does that, it should be immediately revoked a dns record and its owner put on probation, at the legislative level.