In my experience, the rear IR port on Sony displays is a little weird. It's like they used the ring and the sleeve of a TRS plug, not the tip and sleeve.

If your code works with the emitter on the front, get a mini plug and try the rear port again - but after you've seated the plug all the way, pull it out very slightly, and see if it works. You won't want to leave it that way, since it's not super stable, but at least you'll know it works.

Sn@p sells these little TRS plugs with screw terminals, and with those you can put in a jumper to effectively make a Tip/Tip/Sleeve plug.