The upper-left corner of the "page content" slightly overwrites the
upper-left header field. Do I need to "tweak" things just a bit more?
Would I use a value less than or greater than 0.25?
Honestly, I have no idea. It works for me (for now). Feel free to tweak and report your findings. Myabe I've done some thing worng.
Also, there is a bit more "space" below the footer than above the header.
Maybe something is wrong with my printer?
I would say there is no thing wrong with the Hard-Ware. In my (limited) experience, it is gnerally human-error (or some such thing). keep Tweaking and I'm sure it will work.