The distance of the sensor from the bus master has no impact on the response time of the DS18B20 conversion. The DQ line (ie,1-Wire bus) is only transmitting the conversion result that occurred on-board the DS18B20 IC. It is more likely that there is some difference in the insulation/waterproofing of that particular sensor that is allowing thermal conductivity to the DS18B20 through either the package or the GND pin. Keep in mind that the GND pin of the TO-92 package is directly connected to the die of the DS18B20, so if there is close or direct contact of the GND pin to the temperature being measured, then you can expect much better response time.  Sensing through the package of the DS18B20 is of course possible, but thermal conduction is much much better through the metal connection of the GND pin to the die inside the package.