ZirjoGondar:
I play exclusively on my phone. I have had best results dinging the meter by resting my thumb on the bottom edge and resting my middle or ring finger on the top edge, and using my index finger to hit the ding. It helps the brain calculate the hover distance better when the reference plane is between two other fingers (or digits), I think. Works whether the phone is resting on a table or if held by the non-playing hand.
I also am exclusively on my phone, I looked at your post and thought this was brilliant. I went and tried it and worked well at first But then started to bother my finger. I then went back to how I hold the phone and realized that I am doing something very similar, which I am already comfortable with
i have also tried using a stylus and found that I can swing and set the stylus tip back on the screen (without pushing) and then push it for the ding pretty okay. Probably not as good as my thumb since I use it all the time, but plan on practicing with the stylus. There is potential there.