My policy is generally to get things out on the table and not let things build up. I can't pretend I understand this conflict avoidance because I don't see getting issues out and talking about them as conflict. I'm sure you can see how it would get old to always have to be the person who starts the conversations that have conflict possibility because others won't or can't. And I don't really know if conflict avoidant people see how much conflict they actually cause by putting so much energy into wiggling out of what they don't want to deal with.
What I think happens with us e9s is that we unconsciously learn early on that "getting things out in the open" is unhelpful. That isn't true, of course, but that's what Enneagram is about: the stupid lessons that we learned based on very early experiences. Those lessons are so ingrained, we often are unaware that they're being applied in the here and now.
As an INTJ e9, the e9 side gets reinforced even in the present day. Always and everywhere, people object to my more INTJ-ish observations, because those observations completely contradict what they "know" to be true. People don't react well to that, at all, and will inform me that the problem is, of course, with me, since they find no value in my observations. So there is a constant message to INTJs that we shouldn't speak up, and while e8 and e1 INTJs will instinctively reject such messages, those with an e9 fix will tend to absorb them.
What makes a difference is how much experience I have in dealing with such things. In work situations, early on I was easily intimidated, but with experience I figured out how to be forceful (very forceful) in a very gentle e9 way. Being aware that facts can offend people, phrasing them in such a way that they lose their emotional impact and aren't used as a rhetorical hammer actually makes them more forceful, as then the readers/listeners will absorb them without attaching the personal meanings to them that make them easy to reject.
In personal relationships, this is much more difficult, as I don't have as much personal experience in that regard, and removing the personal elements is essentially impossible. Therefore, if I cannot figure out how to phrase things in such a way as to get those with whom I am intimate to listen, I'm stuck. If I say something, I might end a relationship that is otherwise quite strong: there are some things not worth fighting over. But as you've already noted, that's a real problem: if I cannot say something and be heard by the other person, is that really a good relationship?
This isn't to provide excuses as to why e9s do it. You are clearly correct and facing things head on (without going overboard as an e8 or e1 might) is the correct path. Rather it is to point out the unconscious reasoning behind e9 behavior: in our early experiences, arguments and confrontation rarely concluded with favorable results.
