You can have a totally gap-free geo with "force all adges" enabled and the other 3 options disabled. Though you may not like disabling "fully adaptive" since that allows you to increase polygon size over distance.
I figured this out when exporting geo for an external project. There I set up a camera with orthographic view, thus fully adaptive not being important.
Another important finding was that with multi-threading you get many overlapping edges/vertices (can't remember which exactly) at bucket boundaries, thus I had to render the micro exporter images in single-threaded mode.
At least it gave me gap-free geo for export, but whether if this is useful for rendering a fully detailed scene with all the bells and whistles I doubt heavily.
Perhaps you can try enabled force all edges and increase displacement tolerance?
You have probably tried that already...