One of the first things we learned about guitar was that our left hand finger tips go right behind the frets.
The real scoop is that the left hand has to exert enough pressure so that the string does not move when it’s plucked by the right hand. There has to be a firm break over the fret. When we place left hand fingers right behind the fret, this is easy to do and takes very little pressure.
Unfortunately, it doesn’t always work out so nicely. When two or more fingers have to crammed onto the same fret, one finger might not be able to snuggle right up behind it. The result is an unclear sound or fretbuzz.
What to do? It’s simple: the finger that has to be positioned farther away from the fret just takes a little more pressure to overcome the string motion caused by the right hand. Knowing this can instantly improve a tough chord’s sound. All it takes is fine tuning the pressure of each finger.
There is such a thing as perfect left hand finger placement, but sometimes situations necessitate a less than perfect placement. Fine tuning left hand pressure is a way to make a good sound out of a less than ideal situation.