I think you need to reduce the sensitivity of the toner to pinpoint the break. Does the sender or receiver have an adjustment for this?
Yes, the receiver has an adjustable volume control that also functions a bit like a squelch on an old-style radio. It also has two distinct tone types it can generate. I'm pretty sure I'm at the limit of the equipment I have - and I've isolated the spot within a 3" or so radius.
I think that's about as precise as I can get within the technical limitations of an RF tracker/toner.