The majority of corners are headed clear rather than scored, so the phase that follows the first contact is where most set piece chances are created. Teams that organise for it convert far more often than teams that only design the delivery.
Clearances land in a predictable area
A defensive header from a crowded six-yard box has limited direction and distance. It tends to travel back towards the delivery side or into the zone just outside the penalty area.
Because the landing area is narrow, attacking teams can station players there deliberately rather than hoping someone reacts first. The positioning is a design choice, not an accident of who happened to be nearest.
Defending teams know this too, which turns the edge of the box into a contested zone with its own marking assignments separate from the ones inside the area.
The player at the edge has the best shooting angle available
A ball dropping around the penalty spot arrives with defenders facing the wrong way and the goalkeeper's view obstructed by the players in front of him.
A first-time strike from there is difficult to save because the keeper picks the ball up late and cannot set. Attacking teams therefore prefer a striker of the ball in that position over an extra body in the box.
The trade-off is one fewer attacker for the initial delivery, which is why the decision depends on how many defenders the opponent commits to the six-yard area.
Rest defence is the other half of the problem
A corner leaves a team committed forward, so the same loose ball that creates a chance also creates the opponent's best counter-attacking opportunity of the match.
Teams typically hold two players outside the area and one deeper still, positioned to intercept the clearance rather than to chase the counter once it has started.
Winning the second ball is therefore both an attacking and a defensive action, which is why the players assigned to it are often midfielders rather than the tallest available.
Defending sides attack the same space
A defending team that clears without a plan surrenders possession immediately. One that has a designated outlet can turn the clearance into a break.
The common arrangement leaves one attacker high and asks the clearing header to be directed towards the touchline on that side rather than straight up the middle.
Directed clearances are a coachable skill, and they change the outcome from a fifty-fifty contest into a possession the defending team can keep.
Repeat deliveries compound the advantage
A team that recovers the second ball can deliver again into a defence that has not reorganised, with markers still recovering from the first contact.
Successive deliveries into a disorganised box are among the more productive attacking sequences available, and they explain why sustained set piece pressure looks so dangerous.
That is also why defending teams place such value on clearing distance rather than direction alone. Getting the ball out of the area buys the seconds needed to reset the marking.