Nioh 1 - Unlimited arrows bow farming

I'm farming the chest in the yellow plane on floor 129 using this method for a Takemikazuchi unlimited arrows bow and I'm losing my mind. I'm using a full Swallowtail set, 25 luck inherited into every piece, yata mirror and another accessory with ethereal drop rate B (best I have), with Gyokuto primary (looting the chest while in LW) and Itokuri secondary and the ethereal drop rate is atrocious. Maybe 1 in 20 is ethereal. I'm starting to doubt that luck or ethereal drop rate work at all when looting chests.

Anyone that has tried both ways knows if it's better to farm Marume Nagayoshi on floor 570? Or maybe I'd get more ethereals from this chest on higher floors (I've beaten 999 so I can farm any floor if it's better)? I've been at this for 4 hours and all I've got to show for it is a Susano bow.