The Mantis...err...Sphinx position is not required to excel in the Madison.
The Madison is already organized chaos. Add the fact that you are new-ish to the Madison, you might be racing with a mixed bag of experience in your local Madisons, etc...I honestly wouldn’t focus on the Sphinx position. It’s not gonna be the difference between winning and losing.
The level of comfort with the bike, track, race, and field has to be all 10/10 for the Sphinx to work well. Outside of that, you have bigger fish to fry