Thanks Dharmakasi,
The tables enhanced via AET are generated as table types and are inserted to structure CRMXIF_BUSTRANS. In my case, the Z tables are already defined and would share with other custom applications that I have to redefine the backend processing to synchronize updates to my Z tables. Manually extension from GenIL layer is still preferable as this solution is generating dual storage in the system. I would continue to strive why the READ_ATTRIBUTE method is not invoked.
Jackie