We have all seen this picture of the tongue in our grade school textbooks Each taste receptor has its own place and never crosses into another. This was based on research performed by a German named D.P. Hanig in 1901 and went unchallenged until the 1970's. He essentially tested himself and a few friends based on verbal reports of tasting different foods, less then scientific. Modern day research shows us that there are tastes buds specialized for different flavours but equally found across the tongue.
Don't believe that I am right? Get out the salt, take a pinch and place a little on the tip of the tongue and all the way back in the blue/ bitter area. Both will be just as salty, feel free to stop reading and go wash your mouth out now.
What does this have to do with whisky? Move that whisky all over the tongue when drinking, not because the back of your tongue can't taste the sweetness in the whisky, but to give every chance possible of those flavours to get into as many taste buds as possible