Use symbolic links to move synched Mobile Applications to USB

To make space on my MAC's SSD, I used a symbolic link to move my Mobile Backups from the Library on my system drive to an external USB drive. This works great. Now I'm trying to do the same with the Mobile Applications folder (which is huge). The symlink works fine for moving, deleting, adding files in finder. BUT, when I do an iPad backup, iTunes says it is copying applications to my system drive, but when I look at the symlink, the new/updated applications are not there. Any clues how to do this? Why it works for Mobile Backups (in the Library) but not Mobile Applications (in my iTunes folder)?