I guess 20 is fine too.
I alway looked on this as a simple reaction.
If you have gas coming from main tank with 20psi pressure you are putting more force on needle valve. Meaning that you have less room to "play around". Each twist is making big difference since there is 20psi behind valve. If you have only 10psi behind valve then you have less stress on the needle valve and more room to "play around".
This is just my plain understanding.
Join as at
www.njas.net 