I've had sensors miss my SS, no matter how I position it over the wire.
One solution: get one of those rare-earth magnets designed just for such problems, and stick it to the bottom of your oil filter. 1) it'll pull any ferrous metal shavings out of your oil and trap it in the filter, 2) it'll significantly increase your magnetic footprint, thus tripping those sensors.
Here is something along these lines, though it's not designed to stick to the bike magnetically. I wouldn't want to trust an adhesive, especially on something as vibey as a Duc twin. A good strong rare-earth magnet stuck to the bottom of the oil filter is what I would try.
Another thing I've done: when a cager pulls up behind me and the light skips me, I will roll forward until I'm almost (or partly) into the crosswalk, then turn around and wave the cager forward until they're over the sensor. Done this a few times. I got a weird look from a couple of the more clueless drivers, but one or two appeared to understand (fellow motorcyclists, perhaps?).
One thing I've learned in web research is that the inductive sensors don't detect static magnetic fields. They detect a change in the inductance of the coil when a large amount of metal is nearby. So... the strong magnet on the bottom of the bike could work, but it's only doing something if you're moving. Once the magnet sits still, it's no longer altering the inductance of the buried wire loop. So... even with the magnet, try rolling your bike back and forth over one of the seams. Moving the magnet over the wire will induce a (small) current, triggering the sensor.