When you say line of sound do you mean the LOS on the TMA plot or the bearing line on the navmap? If you have two bearing lines on the navmap that intersect (say, from the tail and a sonobuoy), then yes, where they intersect should be about where the contact is more or less, allowing for bearing errors inherent to the sensors. The inaccuracies of the sensors create what's called an "area of probability," or AOP. The angle of the intersection also contributes to the size of the AOP.
Also keep in mind that intersecting bearing lines don't mean you have a merged track. A merged track is one that has been tracked on multiple sensors, and then merged into a single NTDS symbol on the navmap, with tracking/indicating (course/speed) information shown in the contact summary box. I don't believe you can merge sonobuoy contacts, although aircraft will link them out as what look like merge tracks.
Now, if you mean the LOS lines on the TMA plot, then no, the target is not necessarily located at the intersection of the lines. The intersection can mean any number of things depending on yours and the target's course and speed, and the relationship between them.
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