I just figured out why these config changes were not working for me, so maybe it will be the same reason for anyone reading this.
Having MAS installed was making the JSISetInternalCameraFOV and InternalCameraTargetHelper modules non-functional for my DE_IVA Extension IVAs.
Uninstalling MAS fixed the problem, as I didn't need it anyway. If you are using something that requires MAS, then I don't think this config change will work.
Hope this helps someone.
p.s. There's an open issue on the MAS Github to add support for the mentioned classes above: https://github.com/MOARdV/AvionicsSystems/issues/353
Hopefully that gets added at some point