If the distance is 0, the compensation is 100% transferred to the disturbance zone. This requires the noise source to be as close as possible to the capacitor, much smaller than λ/4. In practical applications, this distance is best controlled between λ/40~λ/50, which is an experimental data.
For example: 0.001uF ceramic capacitor, if the total parasitic inductance is 1.6nH after being installed on the circuit board, then the resonant frequency after installation is 125.8MHz, and the resonant period is 7.95ps. Assuming the signal travels at 166ps/inch across the board, the wavelength is 47.9 inches. The capacitive decoupling radius is 47.9/50=0.958 inches, which is approximately equal to 2.4 cm.