Asset bundle question, apk file size didn't reduce

Since one of my character’s size is big (the .fbx file, 4Mb), so I want to use the “bundle” to load it from outside to reduce the apk file size (for android platform). My step is:

1, Add an source file contain the code “BuildAssetBundle()” to editor

2, In “Project”, find this resource file

3, Use the menu trigger code of step 1 to output .unity3d file

Result, after I delete the resource file and its dependencies, the apk file’s size isn’t change, but I thought it should reduce the size.

What’s wrong in my steps?

Find the reason, the big file on PC isn’t so big after unity compiled. The editor’s log has information of most of the resource size. If want, check your editor log.