Wanted: Surly Dingle Track Sprocket

Isn't the idea to run one with a double chainset and so that the number of teeth in each "plane" add up?

I always thought it was for a single front ring? If you have two then you might as well get a derailleur.

Do you think it is rubbing because you are using a 1/8th chain. It is designed for use with a 3/32 isn't it? The thinner chain would probably avoid any rubbing. Does it work out that the chainline is correct with the inner/larger sprocket, and a few mm off on the outer or is a standard spocket offset in line with the middle of the dingle... in which case each sprocket is a couple of mm out of alignment in each direction?

Is it better running on the larger or smaller sprocket?

The chainline is better on the inner ring, I think with thinner chain on the inner ring it would be totally fine. I'm getting into territory I know nothing about here, but I think chains designed for geared bikes have flex in them, so the chainline doesn't matter as much as with a track chain. Maybe worth looking into.