PE with BASH_SOURCE doesnt seem to work

[alex xmb sw ratchev]

i like do shorts , so i tried
the point is ' prepend PWD to BASH_SOURCE when it doesnt begin with a slash
'
but it doesnt seem working

shopt -s extglob
f=${BASH_SOURCE/#!(/)*/$PWD/&}
declare -p f

~ $ bash tbash1
declare -- f="tbash1"

~ $ bash "$PWD/"tbash1
declare -- f="/data/data/com.termux/files/home/tbash1"

the ' bash tbash1 ' case it is , it doesnt prepend anything
( i also tried [!/] instead !(/) , same result )

greets