See https://issues.liferay.com/browse/LPS-71043 for details. Use default images for default user avatars instead of initials, since initials are not used in some regions.
For now the portal property approach must be documented. In the next release there will be a User Images entry in System Settings where this will be configured, but the portal property is the only method that will work until then.
See https://issues.liferay.com/browse/BPR-9072 for release timeline (probably FP 13, tentative date March 21).