Gotcha. I was wondering your setup. It's not very efficient forwarding packets to the FW anyway.
I wasn't impressed with the E3200 setup. Lots of glitz without much meat and geared for consumer 1-click setup (like bridge mode). Last thing we needed was a file sharing USB drive. But my boss bought it as a quick AP and I got stuck making it work.
It's been solid for a few years so I'm not complaining. I thought I saw some 3rd party firmware that may help, too. Good Luck!