The Default Trust list is essentially meaningless to you if you have your own custom trust list. Even adding a single person to your custom trust list will remove Default Trust for you, and so their feedback becomes untrusted unless you manually add them to your own list.
I don't think this is still correct, and I've just tested it: as long as you add "DefaultTrust" to your Trust list, it's included on your Depth 0, which means all DT1-members are included on your Depth 1, and all DT2-members are included on your Depth 2.