The most important thing about Fenshan is the context behind it. If it is cut off by other graves, it is naturally not good.
But nothing is absolute. If the situation is too hasty, it would be better if someone supported it at the back!
Of course, the most important thing is to pay attention to whether you have reached the dragon cave!
Back to your question: In theory, no one is allowed to build a new grave behind the grave, which will break Long Mai and block the dragon's breath, unless Long Mai does not come from the rear, because some Long Mai comes from the front or left and right. Long Mai also has plains, but most people can't tell them apart!
If it is your own grave, you can't build a new grave behind it, because future generations can't be above their predecessors, they can only flatten it or lower it!
For reference only!