I get best results by doing the opposite: when I put more pressure on my index finger, my bare shafts fly with a lower nock than when I put more pressure on my ring finger. In general, the recommendation is to put the most pressure on the middle finger, less pressure on the index finger, and least of all on the ring finger. However, the overriding recommendation for everything is to be consistent. I tried for a while increasing the pressure on my middle finger and got inconsistent results, so I went back to the way that was most comfortable for me, which may be more than the recommended amount of pressure on my index finger.