r2 or R2 in metrum 2/4

[Albert Einstein]

Does the mark of the rest in case of pause in whole duration of bar 
independently of metrum (2/4 6/8 4/4) look the same and is centered and 
under fourth line?
R1 for 4/4 ?
R2 for 2/4?
R2. for 3/4?

Is it the truth that small r is used to put rests beside pitches in the bar?
And that R is used for pause in whole durtion of the bar and looks the 
same for any metrum?

This questions are maybe strange but I can't find this theory.

Albert