Model size:
Amount of memory needed for decompression. Must include buffer size, plus, size of index table.

Largest optimised match:
Max optimize lookahead for Optimal Parsing. Zero disables optimizing. Note that looks like with zero param. WinRK uses a different structure for match search (hash chains?). Some testing results with world95.txt:
0: 561,889 bytes
1: 615,367 bytes [!!]
2: 610,408 bytes
512: 505,151 bytes

Audio model order:
Not used with ROLZ2.

Bit-stream model order:
Also not used with ROZL2.

Other options are self explanatory.