how to achieve that attributes etc. from subtypes are rolled up to one single table?
Implementation of elements(types) of entity hierarchy depends on "Engineer To" flag - if it's set for related relational model then enity will be implemented as table. So for single table you need that flag set only for super-type (or root of hierarchy) and not checked for all subtypes.
"Subtree generation" is not a property, it's functionality allowing easy set up of "Engineer to" property for edited entity and its sub-tree. This is why it's always on "Do not preset".