Good answer techinal answer earlier.
More simply. I will try!
There is a relationship between effort and wind but it is not a simple portional one, there is a square law involved. ( Or something simular)
Because of this greater effort is required to increase speed into wind restence or air resistance as the speed increases.
Ie if you double the power of a truck it might only go +10 mph top speed or say 15%. However if you doulbed the power of a truck that could only max 10 mph the increase would be more like 80%
Another factor is the fact that bikes present differently at each end. Ie thay are not javerlins!
At slow speeds you may get proportinal more benifiet from a tailwind if you sit up and act as a sail even though this increases drag. At higher speeds in the same wind this would slow you down as the effect of air resistance is higher than the benefit of the sail effect.