HC12-Module transmission power decrease and increase

I want to decrease and later increase the range of my HC12-Module to a certain point with the “AT+P<1-8>” command. When i tried it the HC12 sent a “OK-P<1-8>” and when i checked it showed me the right configuration. But while testing i realized that it made no difference for me if im sending at the highest transmission power(+20dBm) or the lowest (-1dBm).
So my questions are :

Am I using the “AT+P<1-8>” correctly ?

Should there even be a noticable range difference from -1dBm to 20dBm?

Any tips on how to solve this?

Thanks in advance

How far apart are the HC12s you are testing?
If they are line of sight then you are unlikley to see any differance.
You need a large distance like several KMs to see any differance.

Should there even be a noticable range difference from -1dBm to 20dBm?

At the point of failure then yes.

In a given sitution if the range at which comms failure occurs at -1dBm is 1 distance unit, then at 20dBm the comms should fail at 11 unints.

So if you had line of sight and the range at -1dBm was 100m, then at 20dBm the range would be 1100m.

Do appreciate that in a lot of places in the World its not legal to use 20dBm (100mW) in the 433Mhz band, your limited to 10dBm (10mW).

the RF guys #1 mantra: "Solve radio problems with antennas first, then increase power"
the RF guys #2 mantra: "$1 spent on a better antenna is worth $10 spent on more power"