Change in the state of delivery
A strong change in the market structure is an important signal. Especially when it originates from a longer timeframe level, but how could you possibly know that a new low won't be reached?
You have to observe a shift in the current condition of the delivery.
When evaluating a CSD, you should focus first on Time, then Delivery. A price-fully filled fair value gap is an example of a capital structure defect (CSD).
You can tell from the charts that the gap was not completely filled, which indicates that the BOS probability is low.
It is true that if you wait for the gap to be closed, there is an entry that you will miss the opportunity to enter at the bottom, but take a look at this example.
You have two options for entering the trade: either enter aggressively on the reversal or wait for the gap to be completely filled before entering on the second order block.
That is technically a continuation entry, and entries like these have a higher probability.
