1degree variation is nothing really. How are you monitoring the temp swing(digital thermomoter) The size of the tank, size of heater placement of heater, Water flow around the heater,Lights, room temperature, all affect the temperature swing.
My house thermostat is always the same temperature 75 roughly. I have just 1 200watt Jager in my 46g tank Placed right in front of my skimmer pumps intake so the heated water flows threw the skimmer and gets distributed into the tank. It is set at 77degrees I measure the temperature using a floating glass thermometer it is at the 80degree line everytime I look at it. Really consistent. Very little swing and It really doesn't concern me if its 82 or 78 as long as it is consistent within 4degrees.