Connect the RPi directly to the projector and I'll take an educated guess that the 1/4 screen issues go away. Then if you add spliters and adapters etc. inline the issues reappear and you'll know the self-inflicted cause.
I'm not expert on config.txt options but I doubt the HDMI tweaks you added there do anything. Almost all the old firmware tweaks were obsoleted when RPi switched over to the upstream kernel display pipeline (some time ago). Many of the old tweaks have kernel DRM equivalents though.