In reply to dave_59:
I should have commented on my own question.
The problem was --parameters were not of same type. Once that change was made, had to import a package in the test for that particular item type.
After these two changes, factory did override the extended class.
In above example a_sequence_item was suppose to be b_seq_item, and it had it’s own pkg(b_pkg), which needed to be imported.
The base_seq class was created in the env using parameters b_seq_item & d_item.
Thanks for commenting back.