The post_migration.bat file should work for XP to 7 migration. It runs after the first reboot and after the 17 or so series of steps while the user is locked out. Can you run the .bat file manually after the migration, and does it work fine then?
For the base layer provisioning, you use the post_provisioning.bat file. We need to document this better.
Make sure both files are a part of the reference machine while the base layer is captured and put in the proper folder.