It's different for everyone (different hand shapes and sizes), but what worked for me was rolling my wrist towards my thumb so that the side of my index finger is what was pressing down on the fretboard instead of the bottom of my finger. It's not roatated that much. Like, if your fingernail is 12 o'clock and the pad of your finger tip is 6 o'clock, I rotate my hand enough to press down on the fretboard with with about the 7:30 part of my finger.

Also remember you only need to make contact with the fretboard where those strings play. So just 1, 2, and 6. You don't need the middle 3rd of your finger to press down. So arcing your finger helps a lot. You need a strong press with the bottom 3rd of the finger, and strong press with the top 3rd / tip.