Why isn't CALL QSYS.QCMDEXC('WRKACTJOB', 9.0); working but CALL QSYS.QCMDEXC('WRKACTJOB', 000000009.00000); is?

So from what I read QCMDEXEC takes two parameters, a command string, and a
length. I don't particularly want to call WRKACTJOB, but it was just a
simple example that would work on any given system. Anyway in this
particular case the command fails unless the 9 is preceded by 8 zeros and
suceeded by 5, which I guess explicitly forces the decimal to be (14,5).

Now the second parameter is a decimal(15,5), and the way I understand
stored proc parameters, either the value gets cast to the type the stored
proc wants, or it doesn't. On top of that, a string length has to be a real
number. Characters are atomic in SQL (and everywhere that isn't bizaro
land). So why is the parameter not an int or bigint, and why must it even
be specified?

Thanks,

Justin