Vandersteen 1C Tweaking distance to front wall

Hi
Looking for any experience and thoughts from Vandersteen owners on your setup distance to the front wall.

The back edge of my 1c's are currently about 23" distance to the front wall.
Speakers are 7.5 feet apart and i sit about 8.5 feet away.
At moderate volume  and with good recordings the sound is fabulous with good controlled full bass.

However I tend to listen a lot at low volumes late at night and listen to lots of older recordings as well. Both these factors contribute to the sound being a little lean sounding down low. I'm considering moving them back closer to the wall to tweak up the bass frequencies. 

Any thoughts or how far are yours from the wall ? thanks