The way a single sostenuto pedal can transform a chord

I spent the better part of today's practice trying to get the voicing right in the middle section of the Chopin Nocturne in C-sharp minor. The sostenuto pedal holds the bass note while the rest of the harmony moves over it — it's like time suspends for that one note. I finally felt it click for a few bars, then lost it again. That's the work.