For me, I am using POE Passive Injectors as attached. And they work fine over 20 meters length.

As I suspected, passive PoE works if you have a splitter at the camera end to extract DC power to feed into the camera's 12V input (as you have done). A PoE setup that conforms to the 502.3** standard does not need a splitter because the camera takes power directly from the ethernet plug.