@ eossette
It means that you can use second curtain sync so long as you don't try to enable ratio control. With "Wireless control" disabled, the YN-622C behaves like a Pixel King, with all slaved flashes set to the same setting. If you have "All" set for ratios, then there is no need to enable Wireless control because it will behave the same with it switched off.

There is no such thing as mixing optical wireless mode with these radio triggers. The camera thinks that the YN-622C transmitter itself is a flash, so what the camera thinks is optical is actually 2.4GHz. For this very reason, if you have a 5D Mark III or 650D, you need to set the camera to optical transmission (vs Canon EX-RT) for the Yongnuo system to work.

If you put a flash on top of the transmitter, it is not actually getting information "passed through" from the camera. It's just another wireless receiver that happens to be on your camera. An on-top flash is not really any different from any of the slave flashes.