Yes, it has to do with the beam height. You're seeing "sleet line" at a certain distance away from the radar because it's where snow aloft is melting into rain and refreezing back as sleet few thousand feet above the ground. Think of it as a mix zone with snow, rain, and sleet. The closer you are to radar, the lower into the atmosphere the radar beam is hitting so it's seeing mostly same stuff again (which is sleet in this case).