The hoe does not flatten ground perfectly, and the gaps between a piece and the ground can be invisible. If a piece is not blue, it is not grounded. The devs could fix this with fuzzy logic, but that could result in builds where if you hunker down you can see that a blue post is floating barely above the ground.

You can use clipping to force a structural post into the ground by attaching a smaller post and blending, but idk whether this translates to blue all the way up. You could also use the raise ground feature of the hoe, raising and flattening until you get blue. You have to do this for every structural piece if your build is ambitious.

Imho, the build system could stand a complete re-thinking. For instance, we can only rotate pieces in one dimension. There is no way to create our own pieces and add them to the sub-assembled pieces. I hope the devs will not spend any time debugging the current system, but I hope for a lot of things.