How to use the procedure to Determine the Correct amount of RF Preamp Gain?

I have the published procedure to determine the amount of rf preamp gain per band and conditions.

I must be doing something wrong because as I would expect with a calibrated S meter changing the gain doesn't change the dbm value because the power of the received noise as measured at the antenna input doesn't change, since it is calibrated to measure the power of the signal at the antenna jack. The only change I see is the level of the noise flour as indicated very approximately by a jagged line against a vertical scale on the right hand side of the display. But the S meter dbm value essentially remains the same since it represents the unchanging background noise power.

Is my mistake in assuming the dbm value is that which is displayed on/in the S meter or the slice receiver? Is the dbm value you are referring to is the noise floor value on the scale on the right hand of the display?

Thanks

Phil, NC3S