cats_five said:
I mean from about half-way along the length and 1/4 in from one side. The speakers are about 3m away.
Does that mean that one speaker is further away from you than the other? As a rule of thumb, you want to have both speakers the same distance from your listening position and the same distance from the front and side walls. Otherwise you can end up with one channel being delayed relative to the other one, more sound reflected from one side wall than the other, more boundary reinforcement on one side than the other etc. You then have to either deal with these problems or put up with them.
The "rule of thirds" as applied to speaker and listening positions, has more to do with acoustics than aesthetics, but the idea is the same as with photography. It calls for the speakers to be placed one third of the way along the diagonals of the room. Your listening position should then be half way across the width of the room, along a line which intersects the two thirds positions. This is usually quite successful in determining a good sounding listening position, but with a smaller speaker, you will normally get better results by moving the speakers closer to the front wall. Moving the speakers closer to the wall does two things. It allows you to take advantage of boundary reinforcement, to support the bottom end. This is probably going to give you a more satisfying end result. It also pushes up the frequency at which speaker boundary interference from the front wall reflections causes a cancellation effect, which will usually make it less noticeable. The other benefit is of course that you will be tripping over the speakers and cables less often.
The centre of the room is best avoided. Without a lot of acoustic treatment, you will always get pressure building up halfway between any two parallel surfaces. You will no doubt have spotted that this contradicts the rule of thirds dictate about sitting halfway across the width of the room. The reason for this is that, all other things being equal, this is normally a better compromise than sitting off axis or losing the symmetrical speaker positioning.
In reality of course, real rooms are not simple boxes. Their various surfaces are made of different materials and they are filled with a variety of furniture and other stuff. Because of this, the models really only provide a guide. Some measurement or a lot of experimentation is required to get the best results.