essentially what you did was stiffen the front end up and take away steering by doing the front tuning changes. by changing th oil at the rear to alighter one you made the rear steer better by having the weight shift quicker. lighter rear oil takes away front understeer. so essentially you found the right setup.
just run what works.
usually smaller tracks require softer tires at the front for more steering. this is a very general statement though and depends on driving style also. i like a very steery front end