Mean-Reversion Entries Without Same-Bar Fills

A z-score crosses the entry band at the close of bar 20. When is the entry filled in this course?

• At the close of bar 20
• At bar 21's open or mid
• At the close of bar 21

Why is the next price after a mean-reversion signal often already closer to the mean?

• Because the exchange corrects prices after each bar
• Because the most stretched closes are partly noise, such as bid-ask bounce, which fades by the next price
• Because the z-score is recomputed at the open