More clock and more memory = less hash?

I’m trying to overclock my two 1080 Ti. I’m going up in small increments of 50 on each clock and memory. The first pump increased the has, but the second bump decreased the hash. If the settings are increasing and stable, why would hash go down or have less than the lower clocked card?

On Phoenix I have occasionally seen 51Mhash on Nicehash, briefly, before the system crashed, but that is in a case that does not have wind tunnel-type cooling of a mining box.
It would be fun to see what sub-zero-cooled cooling oil immersion would do for the output. Hey, if you could get 100Mh by deep-freezing and immersion-cooling the cards, it would be worth it on a large enough scale.