Aero maps stop telling the truth the moment you follow somebody

Every downforce figure a team owns was measured in clean air, which is not where races are decided.

A team's aerodynamic model is a map: load and balance as functions of ride height, yaw and steering. It is built in a wind tunnel and in simulation, refined against track data, and it is very good. It is also almost entirely a description of a car driving alone.

Follow another car and the inputs change in ways the map was never asked about. The air arriving at the front wing is slower and turbulent, so front load falls. Because the front wing conditions the flow to everything behind it, the loss cascades: the floor works less well, the diffuser is less effective, and the balance shifts in a direction that depends on the specific geometry of your car and the specific wake of theirs. Not a uniform reduction. A reshaping.

That is why following is not simply a matter of having less grip. If it were, drivers would adapt in a lap. Instead the car has different characteristics in every corner, and the driver is discovering them one at a time while trying to attack.

There is a secondary effect that decides more races than the aerodynamics do. Reduced airflow through the radiators raises temperatures, so the driver gets told to back off or lift on a straight to cool the power unit, which ends the attack for reasons that have nothing to do with grip. And hot tyres in dirty air degrade faster, so the car that spends ten laps following arrives at its stop with a worse set than the car it was chasing.

The regulatory response has been to design cars whose wake is less damaging, and to add an overtaking aid that gives the following car a drag reduction on designated straights. I think the second one has partly obscured whether the first one worked. It is difficult to assess how well a car follows when the passing mechanism is powerful enough to overwrite the answer.

What I would like to see, and never will, is teams publishing a following performance figure alongside their upgrade claims. How much load does this floor lose at one car length. That number exists internally. It is a real design constraint and it is invisible to everyone outside.

Clean air is the most valuable thing on a race track and nobody puts a price on it.