Sorry, i wasn't notify for your message

The place holder is far cause for building an higher tower like that, we have to build it at horizontal save it, replace it at the vertical and then make the définitive save, i think that was the cause of that, but, however the bluprint will be build in an other grid, if you go really strait to where you place it, you have to find it.

Is your planet setting got a large or a small radius ?

My planet is a custom one with a max radius and small height map, so that I can have flat pieces of land as well as random mountains and valleys.

I tried to use a hover car to fly to that area I built the platform, but when I got there, I see the tower but the bottom was somewhere way under ground and only the tower was sticking up from the ground.

Also when I click build, and I see the bounding box way out there, I have no idea what's beneath it, is it ocean, rocky mountains, flat land or a green valley, which if rocky mountains, the physics of just dropping the build and it hitting a mountain ridge could tumble it sideways

i know that actually it's hard to place such blueprint, the only thing i can say it's that you should go high as possible and notice the border color of the bluprint when you place it, from green to yellow, green is a complete in air placecement and yellow is when you touch the ground