This is a bit more complex, i'm sure that if you have 2 & Longer payout period, there must be algorithm in place that most likely will sort Posts according to payout time window! Meaning that Posts that still can receive rewards will most appear here on Steemit Search. If you have many Posts that are still popular throughout the month, they will most likely dominate Steemit Search so less opportunity for upcoming Posts, a week is right for trending Posts