Either the usable range is set incorrectly for Target Strength or Painting is being set to too high of a value.

Repro Steps:
1. Launch Unity Editor Version: 2020.1.0b9.3653
2. Create a Terrain
3. Create a Prefab of a Sphere
4. Select the Terrain then go to Paint Details
5. Add the Sphere as a detail mesh
6. Without changing any painting settings, paint the sphere onto the Terrain.

Actual Results:
The paint brush defaults to being far too strong, either because the range is set incorrectly or the Target Strength variable is being multiplied unexpectedly.

Expected Results:
The Target Strength setting would have a more reasonable range of painting associated with it.

Note:
In the attached image painting of Spheres on to the Terrain appear to be disappearing because it appears the objects are hitting an upper limit and causing an unexpected behavior where the previous painted spheres disappear.