No, your not even close actually
Fill effects the contents of a layer and any effects you have on it as well.
Opacity has no effect on any layer effects you have.
Someone correct me if I'm wrong.
What you described is the difference between some layer blending methods. I prefer to keep it simple there. I use screen for anything that goes "up" and multiply for anything that goes "down".
Multiply does not blend pure white. And it leaves pure black alone. 99% white is blended at 1%, 99% black is blended at 99%. Etc
Screen does not blend pure black. And it leaves pure white alone. Etc.
Think SX here. On a flat background, making a jump that goes from pure black to pure white to pure black - setting this to screen, the effect is a nice gradual transition.
On the other hand, if you want to make a depression, going from pure white to black to white, setting to multiply, you still get a nice gradual transition, its just down instead of up.
Of course, on a flat base, it dosent make much difference, because most things will turn up nice and gradual on a flat base unless you are really heavy handed in PS. But take the same concept and apply it to a natrual terrain base - and you can see how useful the gradual transitions could be. On the other hand, trying to build a jump on a hill can be pretty tricky as you are building a slope on top of a slope...
Oftentimes theres no real difference between normal blending and screen/multiply - but sometimes there is.
(I think I may have been rambling there - so I stopped typing lol)
FRAUD IS A CRIME SAM!!!
