Scheduling Agreement: Firm Zone = Trade off Zone

Hi-

What is the outcome of setting a scheduling agreement additional data field of "Firm Zone" = to the "trade off zone"?

Currently the Firm Zone = the material lead time (77)

With Firm zone = 77

Trade off Zone = 77

AND

Binding on MRP = 1

Does this now allow changes to be created within the trade off zone (even if it equal the firm zone)??

I want to set the scheduling agreement up correctly so that changes are NOT made within the Firm Zone (lead time).

Do I still need to set the "Biding on MRP" to NULL?

Thanks in advance!