TDP="Thermal design power"... (the amount of designed cooling power to get max cpu performance). ̶W̶h̶e̶r̶e̶ ̶i̶s̶ ̶t̶h̶e̶ ̶m̶y̶s̶t̶e̶r̶y̶?̶

Mystery might be also in the nuance of turbo vs base frequency draw. So even if you design for TDP as the "max thermal dissipation" you might get only base frequency performance.

On a side note people often confuse TDP with the max power draw of the processor. Intel does not specify total power draw probably because processor scaling is such an important consideration. If you have a system, the easiest way to figure out what max draw from the power source is to consult the power brick.