SQL 2012 :: Rebalancing Data In File Groups

I am looking for the easiest way of rebalancing data across multiple files.

Instead of creating a secondary filegroup and then dropping and recreating all indexes in the database which is going to take ages (we have a lot of tables and indexes), I am trying to just add more files to the primary file group and then rebalance data evenly between these.

I guessed that adding the new files to the primary file group and then rebuilding all indexes on a table should redistribute the table over these multiple file groups evenly. This is not the case though. It does rebalance data a bit but I still end up with the majority on the first file that existed.

I have attached the script I am running, maybe it is something in the create database/file statements that is the issue.

Basically what I am seeing is to start off with the table is 160MB. I then add the file groups and rebuild all indexes on the table. The first file is then about 100MB and each of the three other files are about 20MB. I would expect them all to be the same size.