Average item Lv Formula?

[StouterTaru]

2 handed weapons count as 2 slots and 2x the level, and level rounds down.

Im a summoner. No Shields and Im using a Crimson Circlet, soo no Cowl. Lets see 12 Slots Total.
Crimson Lv80
Darklight Tome 55 (110)
Vanya Robe 70
Darklights x 7
Austere tights 60
Demagogue Ring 60
Total 815 (870) / 12 (13) = 67.9 (66.15)
Game says item Avg Lv 66