HC-12 module baud rate questions

Hi!
I have one question: if i have just set the baud rate of both the modules to 1200b (AT+B1200), what does that mean:

  1. The baud rate at which the modules communicate to each other but NOT at which the arduino speaks to the module
  2. The baud rate at which the arduino speaks to the module but NOT at which the modules communicate to each other
  3. Both positive - the baud rate at which EVERYTHING communicates.

I want to try the modules at MAX power (AT+P8, AT+FU4, AT+B1200, /AT+C010 just to test different channel from #1/) to see their range. The first arduino is an Uno R3, the second arduino is actually ATtiny85 chip. Thank you.

Its no 2 , the rate at which you speak to the HC12.
The actual over the air data rate isnt user adjustable, but it does change with changes in user baud rate.
You would need the datasheet to find out, but Im not sure its there.
The over the air range will change because the receiver sensitivity changes with differant rates.
That should be in the datasheet somewhere.

This may help.

Yeah, that makes sense. So, in other words, the way the arduino speaks to the hc12 affects the transmission range?

Yes, for a given transmitter power, the higher the transmitted data rate, the lower the range.
This applies for any transmission channel in the presence of noise.
The maths behind this is given by the Shannon Hartley theorem.