As Panzrwagn describes the situation, the dealer is correct that you will need less acoustic output of the speaker to achieve the same volume level in the smaller room. The question that cannot be easily answered is: will that be enough? If you normally play music at very high volume levels, a small stand-mounted speaker like the Electa Amatour will be stressed and will probably not sound their best. If you like the sound of these speakers with the vast majority of music you listen to at the volume level you mostly listen at, you have to decide whether it is worth while giving up on some head-banging activity. All choices involve some compromises in certain areas of performance.
Does room size affect volume and bass?
I listened to a pair of Sonus Faber Electa Amatour II, I love them, only one problem, when I have one of my Reference Recordings with the Dallas Wind Symphony on, when it is playing loud, like around 90 DB and the bass drum cracks the speaker cone reaches excusion. This was at my dealers room which is 4 times the volume of my 19x13x8 room. He said that if the speakers were in my room playing at the same volume, they probably wouldn't hit the cone excersion. What do you think?