How to sort Artists in ID3 metadata

In BLS-KB13-916 it is stated:

BluOS sorts and updates your Music Library based on the ID3 Metadata Tags incorporated into the encoded music based on Album, Artist, Track and various other tags.

ID3 metadata contains fields like "Album Artist" and "Album Artist Sort", but these fields are not used.

[{
"Album": "Work Song",
"Artist": ["Wes Montgomery","Percy Heath","Bobby Timmons","Sam Jones","Louis Hayes","Nat Adderley"],
"Albumartist": "Nat Adderley",
"AlbumArtistSort": "Adderley",
"ArtistSort": "Adderley, Nat",
"ISRCNumber": "DE-A31-99-01011",
"Date": 1960,
"Title": "Work Song",
"Upc": 4003099919921,
"Cdtoc": "9+96+4B1E+8EFD+C245+11A5C+17022+1BE56+22F2C+2722B+2ACA8",
"CddbDiscId": "7C091E09",
}]

I would expect this album to be sorted by Album artist sort "Adderley" with the display name "Nat Adderley". However in Bluesound's search index this album is by Album Artist "Wes Montgomery" ?! But when I browse the Artist index and select "Nat Adderley" the same album has Album Artist "Nat Adderley". Same album - two different Album Artists.

In the Artist index the late Mr. Adderley is filed under "Nat", which confuses a librarian like me :-|

Can anyone please tell me exactly which ID3 fields are used for indexing - and why the specific sort fields are not used for sorting?!