I'm back to offer this update:
We've finally had another day with the right kind of overcast for me to try out my new lightdim dot. I'm disappointed to find that the 3/4 dot is definitely not enough.
Over my lunch, I peeled off the dot and cut a slightly elongated square from the 25mm X 57mm strip. I applied this across the sensor, front to back (probably makes no difference). This piece didn't do it either.
Next, I think I'll double up the 25mm strip, but running side to side.
I'll come back here to check in and record results!
*Make mine plain vanilla*