I am not sure there is a set distance. But the further away from walls and corners they are, the less exaggerated the low end will be.
Mine are about 2 feet from the back wall. The bass is seems to be fairly accurate for me. But they are small monitors (HS50M) and do not have allot of low end to them. Keep in mind corners can be a true pain in the ass. I would be more concerned with making sure they are not by any corners first.
Then its a mater of listening to music you know well and placing them further and further away from the wall. (I like to use a control for this, so I have my headphones with me at all times.)

I hope that helps, though I know I am no expert on the mater.

Lot of factors to consider before anyone can answer that factually, but, yes, they should probably be some distance away. But you already know that.

What kind of monitors? How loud do you listen? How far away are you from them? How big is the room...length, width, height? What shape is the room? Are they placed in the wide side, or a narrow end? Are they on a desk, or on stands? How high are they? Is there any room treatment?
What are the ceiling, floors and walls made of?

There are a lot of web articles about speaker placement if you search. Most are general guidelines that explain that there is no optimal placement parameters without considering all the other factors. If the walls behind the speakers are absorbent, then perhaps they could be a bit closer than if they are reflective.

Basically...it all depends. Bringing them further away may cause other problems...depending on the rest of the room. You may have tamed the problem from behind, but now maybe you created some other nasty reflection/standing wave issue.

Without hiring an expensive engineer, or learning how to use expensive measuring tools (and obtaining them), and then spending the money to do all that perfectly, all you can do is gather all the info you can about monitor speaker placement, and room treatment. Then, just do what you can to make it as good as possible. If something's not right, you can probably hear it. If you can isolate the problem, then a combination of articles may help lead to a solution...keeping in mind that it's possible that a fix for one thing may create one or more other problems...kinda like "political solutions". :roll:

Of course, you could just experiment and see where they sound best, and may have to come to a compromise between sound and maybe not being able to put them in their ideal spot...if it's in the middle of a small room, etc.

Just something to consider.

Kapt.Krunch

BTW, once you set them where you want them, and learn how to make decent mixes with them...try not to move them.

I just moved a while back, and I'm still not used to mine again. Same exact equipment...different space. More useless CDs while I try figure it out. I was just getting used to them there, and didn't have anything finished completely, but real, real close. Back to square one.

Kapt.Krunch

Here is a current thread on amp placement:
Reflections:
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More on audio reflections and what is being done to live in this constantly moving world:
http://www.crutchfieldadvisor.com/ISEO-rgbtcspd/learningcenter/home/speakers_roomacoustics.html?page=5

I have read that the placement of speakers/monitors should be so that they do not place the listeners head directly into the middle of a room dimension.

If you had a room 12 feet deep and you set your speakers in this room, you wouldn't want them placed at such a position to have the listeners head at 6 feet...as an example.

To that end, it is suggested that the listener position be at a point 38% of the room dimension in question.

All things being equal, not knowing anything about what kind of room you are in or type of monitors you refer to, set your speaker away from the wall half the distance the speaker is tall.

These are suggestions, recommendations for a starting point.

Although when I started typing this, no one was here...now you have even more good pieces of information to help you tune your speaker placement.