Just a reminder to beware making generalizations from small sample sizes. It's a common logical fallacy, especially around here. Correlation does not imply causation, but it does imply correlation. Small sample size correlation, however, could just as easily be coincidence.

I hit the same two sectors with the same ships at the same time all the time. Almost all our trips are just 13->17 looking for motes and crafter materia. 75% or more of my trips come back with grade IV Competence materia. Our FC currently has over 150 of just that one type, and that's with me spending a bunch and trying to get others to do so too.