Just out of curiosity.
I made a very basic app (the whole app is 180 lines long and it uses FuseJS/ImageTools, FuseJS/Base64 and FuseJS/FileSystem). It simply loads some data from a MySQL dB and it displays it inside a ScrollView. No other graphics.
Once installed, the .apk occupied 27Mb. But when I moved it to the external SD I noticed that it occupied 46Mb.
P.S.: I really appreciate that Fuse apps may be moved to the external SD card! Not many apps may do it.