I was concentrating on your desire to vary something with stylus tilt and overlooked your point about the 180 degree offset even when the pen settings weren’t enabled.
This is a fact and it’s been discussed before. It is a complicated area and any changes would affect many brush presets that have been made by people, either for themselves or as distributed bundles.
I think it’s something you have to get used to and take account of when you’re designing a brush preset that has brush tip rotation being controlled by something.
See: