You maybe able to use a higher voltage on the injector end to compensate for the voltage drop to the splitter end of the cable.
As the camera changes how much current it is using. Like in pan and tilt. The voltage will vary.
They do make an Active POE style injector. Many times the injected voltage is 48 volts and the splitter end has a voltage regulator in it. That way the drop in the cable is compensated for. I believe 5 volts 2 amps or 12 volts 1 amp is the standard I have seen.
I have also seen reports of low end active POE kits failing at the splitter end. Resulting in up to 48 volts being applied to the powered device.