Western Altepa Desert Treasure Casket drop rate extremely low.

I've been solo levelling up my THF job with adventuring fellow and Alter egos and I usually rely on the Treasure casket drops for TMP items and Perm items and armors/weapons while I do FoV pages. The problem is in Western Altepa Desert (I don't know about East unfortunately but it might suffer the same problem.) is that out of killing over 100 mobs or more I 've only seen 5 treasure caskets drop out of my entire time there. 2 temporary blue caskets, and 3 locked brown caskets. That ratio is extremely low compared to many other areas and I've gotten more treasure caskets to drop from monsters in Kuftal tunnel runs where it seems the drop rate is proper. I hope that the drop rate for the Altepa area is increased to the same levels as many of the other areas I've been too.