That's what I assumed, but couldn't figure out a way to do so.
And since the 1TB was prepared the same way using the same USB SATA dock, I'm not sure whether or not another dock/adapter or direct SATA port on the motherboard would behave differently.
Thanks for all the work on this!
I already have a working Fat PS2 McBoot/OPL setup on a 1TB SATA HDD via a knockoff SATA "PS2 network adapter" (with no networking capabilities) but wanted to try this "just copy over the ISOs" feature.
Notes on experimenting today:
Using a Xigmateck USB3 HDD...