In practice
The mean threshold is to an order block what consequent encroachment is to a fair value gap: a midpoint to judge the zone by. A bullish order block that holds above the middle of its body is considered intact.
Traders use it to refine entries, placing a limit at the midpoint, and to manage trades, treating a close beyond it as a sign the block is failing.
What to watch for
It is a refinement, not a setup. Price frequently reacts at the edge of the block without reaching the middle, and a midpoint entry on a small candle differs from the edge by very little.