Hi,
Sorry for a long delay and lack of responses in this thread.
During the past weeks, we tried to address a few concerns raised in this thread regarding self-shadowing/shadow-acne. We added two simple mechanisms for that: slope bias (during shadow map rendering), and receiver bias (during the shadow-map fetching). The slope bias is directly controllable per light, and is proportional to the constant bias. With these two parameters in hand (constant bias + slope bias), you should be able to reduce some of the artifacts mentioned in this thread. Receiver bias is setup globally per light types. All types of bias (constant, slope, and receiver) are controllable through global variable per type of lights. These shadow improvements are in final stage of development and will be released with UE4.23
The well-criticized sphere should now appear smoother:
This should also allow to bring a bit more contact without introducing acne (with manual tweaking).
Please bare in mind, these improvements will help but won’t solve all your shadowing issues. Shadow maps are hard unfortunately.