Why Static Batch is not work with Asset Bundle and Application.LoadLevelAdditiveAsync?

I'm make a rts game. Each map in the game is an asset bundle that contains a large GameObject prefab. Most of the GameObject's child objects is marked as Static. But when the asset bundle is loaded at runtime, I find their meshes are not combined.

I guess Asset bundle is not supported by static batch because it is dynamicly Instantiated. Then I tried Application.LoadLevelAdditiveAsync to load the map, and also the meshes are not combined.

So how can I solve the problem. How can I make dynamicly loaded static map really Static.

 

After some experments, I find Application.LoadLevelAdditiveAsync will static batch when running the standalone application.

And the instantiated Asset bundle gameobjects will lost the static properties(all static properties are unchekced), So I can't use StaticBatchingUtility at runtime.