A lot of this could have to do with how you set your flood bars on the white head--I tend to push them in at least a little against the screen--if they are above it by any margin, that will change how it floods, in some cases quite a bit...
Zoo--as far as the ink shelf life goes, I have been told more than once that the resins will absorb plasticizer, increasing the viscosity of the ink as it gets old. It usually gets reduced, and is good enough to print easily, but is not of the same quality as fresh ink.
Hopefully the answer is wrong:since this is the internet, someone should very nearly instantly correct me.