Sorry, I made that about as clear as mud.
It's more difficult on small koi as they are less mature but very strong leading rays often indicate male. As the koi matures, all the rays on male koi become thicker and thus lose the translucency of youth. Females, as they mature, will still have the translucency and usually the leading ray is not as strong as it would be on males.
Btw, this is not the indicator it was years ago. I personally have owned a couple of females that had pecs I would have sworn indicated they were males but both were females and developed eggs.
You probably have heard about the sandpaper roughness on gill plates called Oiboshi. This is on male koi. This will also show as very very small bumps on the leading rays on male koi. It is easier to see on koi larger than 7" though.