Bollinger Bands %RSI

Hi All,
I am not a programmer, but I tried to buid BB% of RSI , base of John Bollinger' book. I cut and paste the function from LazyBear MFI/RSI BB indicator and original BB% scripts. Now, I need help for 2 things :

1. I already check by side with LazyBear indicator for the OB/OS, and all are good. One thing I don't understand is why we build the Basis for bb using "sma" ? any one can help me to understand with this?

2. I am happy with this, but I need to make the Source Price become customisable (close, hl/2, hlc/3, etc). and I don't know how to set it up. please help me with this.

Thank you.