To be more specific, the ruler should be placed in the center-top of your shaft, gently pressed against your pubic bone. Do it this way everytime, for any bone-pressed measurement.
The only measurements I care about are BPFSL, and BPEL.
If BPFSL is increasing, then I know BPEL gains are coming. If BPFSL is not budging, then I would have to refine my routine, either by adding more intensity, or time, or both. Therefore, I check BPFSL once a month, with a set goal of 1/16" gain.
I personally don't care about NBP measurements of any kind, because as long as BPEL is increasing, the rest will follow.
The fat pad will shrink with a good diet and exercise, and has nothing to do with PE itself.
Some guys like to keep track of flaccid length. I don't see the point. After a session, it looks a little longer, which is great. And then I go out in the freezing cold to buy some groceries, and it is not the same anymore. It constantly changes depending on temperature, stress levels, etc. So why even bother keeping track of it? BPEL is what counts at the end of the day. I really don't care about the rest.