Most chart movement is noise. An app drifting a few places on a quiet Tuesday is the normal behaviour of the charts, not news, and mailing about it teaches you to ignore us.
So a move has to be large enough to clear a threshold we set by measuring how the charts actually behave — not by picking a round number — and each app has a cooldown afterwards so a genuinely volatile one cannot mail you every day.
Entering or leaving a chart, and crossing a major position milestone, are treated as events in their own right.