Definition of Voltage Sensitivity in Power Detectors

Hi all,
I have a question regarding the Voltage Sensitivity (VSS) in Power Detectors.

From HP AN-923 "This parameter specifies the slope of the output video voltage versus the input signal power, i.e., Vo = γ*Pi of the diode. It is bias, load resistance, signal level, and RF frequency dependent, and all of these conditions must be specified. It is particularly sensitive to signal level which must be kept well within the square law dynamic range of the diode."

Introduction:
I made the measure with fix frequency and I took the voltage output every 0.25 dB (span from -70 dBm up to +20 dBm).
In order to calculate the VSS, I choose to use two ways: 1) in logarithm scale 2) in linear scale.
In both cases in order to calculate the quadratic region, an observing windows (==n. points) is defined, and a linear approximation is calculated.
Due to the behaviour of the diode, the quadratic region is where the slope has a maximum.

Problem:
Depending on the observing window I calculate a different VSS which varies like in figure:

I was interested then to know which is the correct value to take for the characterization of the detector.

Thanks

It would make more sense to me if the axis of the graph was labelled.
Frank

Yeah, shure!

Y is the Voltage Sensitivity (VSS) in mV/mW in X you have the observing window (points)...