With a EVGA XC3 Ultra Gaming, as soon as I lower the watt limit, the hashrate drops.

Currently the best I could get is ~ 96 MH with HiveOS via the following settings:

-200 Core Clock
+1800 Memory Clock
Power Limit 300W

I wonder why as soon as I put the same settings or different ones with a lower wattage, it plunge.

Any idea why or how fix this?

EDIT: and is this thermal throttling?