+1 more on just behind the fret.
There's a leverage kind of principle happening. Lets say you had to hold the string on the fret with, say, 200g of weight to keep the string from buzzing.
Touching the string right between the frets would mean both frets push back at you with 50% of your force, half each, adding up to an equal and opposite counterforce. So to get 200 grams of pressure at the fret that's being played you'd need 400g of total weight since each fret is pressing back at you with 200g of 'equal and opposite reaction'. So you're tiring your fingers out twice as much as you need to. Worse still if you play far back from the fret, you might need a kilo of weight to stop the buzz.
Try it - see what's the least amount of pressure you can apply to make a clean note at various positions - and you'll know why most of us like to be right up "just behind" the fret.