So this is a small annoyance and probably difficult to change in the system.
It just seems to differ from current standard practices.
Name = User ID/Login ID/...
Full Name = First and Last Name
Last Name = Last Name
I know you can change the labels, and we have on Name, but the Full Name/Last Name is kind of annoying and differs from most form filling practices I've seen.
Typically the name is split into First/Middle/Last and then the Full Name is a calculated field from those. From there you can decide through system preferences to show "First Last", "First Middle Initial Last", "Last, First"... etc.