You’ll find, being right handed, using on readers, Right hand is slightly better, reading with phone, left is better (subjective of course)
so if you want NExT,
Spark 2 - If you have fat or vascular hands, you should be able to easily hide a Spark 2 on the back of your hands. P1 - P5
Personally have my Spark in P11 L
It works well there for me.
Just be warned 
I would call the P11 position “advanced” .
What I mean by that is, get a pro to install it there.