Is it possible you started the Recording at a higher Range and changed it after you started recording? Or started recording at 85 and bumped it up towards the end? YellowFin will display the max range recorded in any given ping.
You can certainly zoom in, but the resolution may be somewhat pixelated. YellowFin has a maximum of 1000 data points (or pixels on the image) per ping.
In the help file along with the HBSI Conveter there are some "Optimal" Range settings for playback in YellowFin.
Robert