Hey! The post reward options are unrelated to the engagement, I would recommend leaving it at 50/50 though since steemdollars are selling at a big premium right now.
It might just be that readers/curators have missed your posts, I checked out your post history and noticed that on the posts you haven't received much engagements were the ones I hadn't read/curated. It could also mean that only curators with less influence have happened to read them and voted them up.
This has a lot of different factors, many curators don't read posts and just rely on reputation to decide which authors they trust with their upvotes. If you have used Reddit then you may have experienced that posts can get some engagement in the beginning but if someone were to downvoted it or in this case not upvote it early in time then it won't make it to the "hot" section and many readers just don't happen to see it. That's why engaging with the community and other members is important and building your following and followers and over time the rewards start to balance out.