I just tested it out, and you need a couple of extra steps in there:
- Create the side by side comp viewer
- Create a side by side timeline window
- Duplicate the layer you want to sync to, drag it to the top and turn the visibility off
- Use the main comp timeline window to scrub and preview
- Use the precomp timeline window to make adjustments on a single frame
Dragging the layer to the top of the main comp ensures that the precomp timeline will sync up as you scrub through in the main comp. Don’t scrub in the precomp timeline window or it will sync up with the precomp that has the earliest in point in the main comp.
Also, it wouldn’t hurt to make a feature request to choose which precomp layer you would like to sync to. Go to Help>Send Feedback
Dan Fredley