If the issue is one story (or one chapter of a larger story), then only post 1/3rd of it.
If the issue contains two or more stories, both of which are the same size, then you can post up to 1/3rd of each particular story.
If the story is part of a TPB, then the rule should be a bit more relaxed - if the original issues are out of print and have been for several years, then the TPB most likely isn't. I'm not saying we should allow posting the whole issue or story, but the rule should allow for this.
We should also a lot more scans, or even full issues, only if the creative team and / or the publisher allow it. This is more for indie or smaller publishers who don't really mind it, as long as it gives them more exposure. You know, the kind of exposure S_D was good for.
In regards to Japanese comics: If the story was printed in a serialized form (like Dragon Ball, Naruto, et al) then we should probably accept full chapters, but not very often. This is so we don't get random posters who decide to post a full manga series chapter by chapter.
Also, posting self-contained stories which are part of a series (like that one about the stray kitten who got adopted and which caused the community to go into cute meltdown) should be fine, since they're available in TPB. Again, single stories... not the full book, day by day.