I have RX1 and they are 55 cm from the back wall...my room is aprox. 4x3 m... and to me this is the minimum distance required for a good sound with them
in my case if they are closer than 55 cm to the wall bass becomes excessive with some recordings...(bass heavy recordings)
However I think there are also other things to consider when evaluating their sound, personal taste, stands (must be rigid), distance to side walls and also the amp (I have a NAD c315)
In my opinion, these speakers do need some care in their placement, they are not "fit and forget" speakers...but if you place them properly... they are absolutely amazing for the money and size, they sound like floorstanders...
Also think the title of the topic is wrong... should be called
Monitor Audio RX1 placement advices