Hi Yang,
This is a good suggestion, much because it does highlight a visual issue with the markers and how they line up with source code. Where the source indentation is very deep, it isn't always easy to see what's going on. Implementing this as shown above probably wouldn't be possible with the current design of NCrunch (the mapping would become too complex), though I may be able to find a more creative solution in the long term.
Cheers,
Remco