Why are some system-provided Objects NOT available for configuring secure Subpages?
Some system-provided objects are NOT available for configuring secure subpages.
The reason is because of how the security model works with the relationship of the object to other objects (parent/child). The security delegation for these objects refer to an inherited access right.
Here is a list of system objects that DO NOT allow secure configuration on [Layout:Edit] sub-page properties.
*Benefit Plan Details
*Cost Plan Details
As an alternative, to accomplish some control over the fields that are defines on subpages, we would recommend to use Display Conditions. To simulate access to sub-pages for one of these objects, please create a ‘Group’ and define a display condition. The page will then display for users that are members of a group.