Hi
You cannot use a Ballnose to get right to the bottom of the slope, its Physically impossible as it has a sharp corner
With a very small Ballnose or a Bullnose tool with a small radius you can get closer and closer but there will always be material left there.
If you model a fillet equal or larger than the corner radius of the tool you are using then it will work.
If you truly want a sharp corner there you can surface the slope with a Square endmill, but this will require very small step-downs and will still leave a poor surface finish
Another option is to use a tapered endmill, but seeing as its an odd angle you wont find an off the shelf cutter to do this
Or you can machine the slope with a 5 axis machine and use the Swarf toolpath.
