I dug through the internet for countless hours to find this one guy that registered just to post a solution he found to Syphon only capturing a portion of the screen in World of Warcraft. I just wanted to bring it to the front as it was seriously buried IMO. It may work for others. In a nutshell, you must right click the WoW app manually, go to info and settings, and check off for it to launch in low resolution mode. Saved my stream.
Here's his post:
Here's his post: