Why don't you weave the flashback permanently into the story? Is it possibly that you could be writing a whole chapter on the encounter or at the event and make it as real story instead of a brief flashback?
In my own stories the chapter length can be a few paragraphs, which takes the reader out from the normal story and plants them into another, and visa versa. I mean you can have for example two main characters, and you do the story from both POVs, yet their stories are separated by time. Like for example, the pair is at the present, and the other one tells and every once and a while their stories get interrupted, or even brought forward as the overall story leads to a culmination point.
Think about the story and how many ways you can tell a story within a story, because at the end of the day, it's what we do and therefore, the flashback and flashforward loses their meaning. It is the overall story that has to have an impact, and the story is never remembered, even if it the Lost, from those tropes.