Because it might be cloudy tonight, I decided to do some indoor testing.
I used my Tec 180FL on a DM-6 mount.
I started with some weaving on a curtain on the other side of the house. I looked for a low contrast area. The lighting was quite low because it was cloudy out. I used the same 6mm Clave as I used outdoors under the night sky. As with my tests outdoors, I thought I saw a brighter image and with more contrast when viewed slightly off-axis. It was difficult for me to try many different areas off-axis because of the DM-6 mount so I mostly concentrated on one area off-axis. Next, I used a 5mm Clave and saw the same. Brighter and with more contrast off-axis.
Next, I used an artificial star. As with outdoors under the night sky, the star appeared brighter and perhaps tighter slightly off-axis.
If I went too far off-axis but still not close to the edge, then I did not get this affect. For me, it seems there is a sweet spot. As I approached the edge, of course the contrast was poor and there were other aberrations.
Next, I used a $5 bill and concentrated on Lincoln's eye pupil. There are white spots inside the pupil. Same thing. Brighter and easier to see the white spots slightly off-axis. This was under low light. Then I shined a light on the bill and I was not sure now that I could see a difference. I assume that is because the contrast was greater. It was much easier to see the white spots in the center.
Next, I printed a resolution chart and tried to find an area with low contrast. That worked but for me the better results were with Lincoln's eye.
My results are not conclusive for me and I don't want anyone to feel I am done testing and only believe that all is better slightly off-axis. But I do have more confidence that what I see is true ... For me.
I did a little more research and found another CN member who mentions better correction 30% off-axis in Claves and he has a 6mm listed in his signature. I am going to contact him to ask if he has seen this affect or if he only read about it in Lord's article. Will be interesting if he responds.