So it looks like this does not follow what we consider to be the normal rules for Eclipse duration. At 35 base duration, we would expect it to give 7 extra duration for each point of bonus Eclipse duration. Instead, it looks like it's actually giving 5, confirmed at both 1 and 11 bonus Eclipse duration. According to Kinak, "Personal Eclipse has its own conditional modifier that looks like it's throwing off your calculations there", so it may be something specific to this, rather than a misunderstanding of bonus Eclipse duration in general.
Personal Eclipse / Discussion
This is the discussion related to the wiki page Personal Eclipse.