The only way to find out is to try it out.
My own speakers are supposed to work 20cm from a back wall. In my room, they are at 60cm. I tend to start with the manufacturers' recommendations and end up with something different.

Every room is different.
Suck it and see old chap, it's the only way to go. A decent dealer will let you do a home dem.
Regards,
Steve.
It's just a pleasure to hear music as it was intended to be heard.