Try this: When you bar a fret, no other fingers just yet, press the strings down half way through (so just a couple of millimeters), so dón't touch the fretboard just yet. When you do this, focus on relaxing your neck, shoulder, arm, hand, everything ('focussed attention' to 'total body awareness'). Keep doing this multiple times, while being as relaxed as you can. Then at one point, gently press the strings down to the fretboard, still making sure and focus on your body to be relaxed. You will find out that you actually need just a líttle bit of pressure to make all the notes sound clean. I was pretty amazed, when doing this the first time. It's worth it to stop playing every couple of minutes 'Posing' (especially when your hand gets tired) and notice what's happening in your body, in this case in particular the neck, shoulder, arm and hand. Is everything still relaxed?
One of Wiley's other points is that the index needs to be placed differently (higher, lower) depending on which strings you actually need to fret. At one point you'll know it instantly and automatically, but you need to experiment with that. For example, an Am-shape barre chord, your index only needs to fret the 5th and top string. An 'arched' or 'curved' bar. It's actually easy.
And then of course, the action of the guitar has to do with it as well. It's worth it to check it out, all your guitars for that matter.
Hope this helps for now. Keep us updated if you will.

Ness