zero*That is the question... Nah, not really. They aren't very adjustable though so it seems to be impossible to get them perfect. Is having the plastic housing anywhere in the notched range ok? There are six notches and with the current mount mine won't go close to center. I can have either just within the first notch (too high?) or on the fifth notch (too low?)... or are both ok?

no

Anywhere in the range is fine and it’s rare that you land exactly in the middle.

I usually pop up the silver tab and push the binding heel forward till it makes contact with the boot heel than push the tab down to lock it in. Click the boot in and recheck that it’s the scribe area and that’s the one I’d use.

Anywhere within that range is acceptable. It doesn't necessarily have to be centered within those marks. I find it's can be a little harder to read than some other bindings. If you are really worried about it take 'em into a good shop and have a release test done at both positions.

Yeah having them anywhere in the notched area is ok. I was inbetween like you're describing and I went with the shorter one, it felt better, longer had just a slight wiggle that went away with the shorter

My notches are kinda stripped. They look like ovals now and my heel slides off allot