I also thought the image was soft at the edge. When I made this comment to the others, Leon Fasano remarked that he owns the same model eyepiece and has not experienced any of the problems I was having. I loaned the set to Greg Lutes and he was very happy with the performance. From everything I had read and other observers experiences, the 6mm should be giving better images than it was. After thinking about this for a time and doing some research I believe that the problem is in my eye and not the equipment.
Telescopes have two pupils, an entrance pupil and an exit pupil.
The entrance pupil is simply the aperture of the telescope. The exit pupil is an imaginary disk just behind the eyepiece through which the light rays pass on their way to your eye. Its size is the telescope s aperture divided by the magnification. What makes this so important is that the exit pupil of a telescope should not be either too large or too small. If it is too large, your eye can not take in all the light the telescope can give.