Notes are your friend in this. Whenever in some observation it’s not overwhelmingly clear what the subject of ID is, I write in the notes what my feature of interest is. Doubly so when the observation is dominated by the species that’s not the species of interest or it’s not in the most noticeable position.
This goes both for image-based and sound-based IDs. For images, what’s noticeable is what takes up most of the area, or what is central. For sound, it’s what takes up most of time time, and what is heard at the very beginning of the recording.
Sometimes people will ignore your note, but in my experience almost always people will adhere to what you say there (e.g. “this ID is for the red bug in the corner, not the yellow one in the middle”).
What I also will sometimes do, both to help with IDs and to make it easier for people to actually check existing observations of a species, is to include a truncated version of the media (tight crop of the subject of interest, or in your case a tight crop around a single NFC in the sound file) and put it as the first photo / recording. That way whoever is checking it out will be clear on what you meant there, and can still use the second, full-size / full-length medium to get richer info about the context, spacing of calls, etc.