Converting from RGB Color Picker to Surface Reflectance

My apology if this question has been asked many times in the past. I went though similar posts but still am not clear on this.

I am trying to derive the material reflectance values from a color picker tool(say MS Paint).
My understanding is to first gamma decode(raise to the power of 2.2) the RGB values from the color picker, so to bring it back to linear space, and then use it in Radiance mat definition.

However in the “Rendering with Radiance” book section 5.1.4 Estimating Surface Color page 295, the rgb values from the color picker are raised to the power of inverse of gamma (1/2.2) and then used as in the material definition.
My question is, should the sRGB values from the color picker not be adjusted first(raised to the power of 2.2)?

For example for BS4800 “18-B-25 Dark admiralty grey / Merlin” colour sample, this webpage shows sRGB=104,112,116 and LRV value as approx. 16%. This matches closely to my understanding of (112/256) ^ 2.2 = 0.16 (just for the green component).

I also tried the above colour sample through the Colour Picker tool by Axel Jacobs, where there is an entry in its database for the above sample(in the chooser tab). It gives “R=0.414 G=0.434 B=0.449” for Radiance plastic material definition which are very close to just the normalized values and without any adjustment for gamma.