Sorry for the double post but I wanted to keep this separate from the list.
Today I tucked in a Klinklang (didn't do Normal since someone else did it and it was added to the OP anyway) and the results were just confusing.
Cave: 35 (43%)
Mountain: 29 (36%)
Sea: 6 (7%)
Forest: 5 (6%)
Manor: 3 (4%)
Sky: 3 (4%)
Cave was the most common, but Mountain was almost as common, so I can't exactly say that Steels favour Cave only. But then Sea, Forest, Manor and Sky were not seen very often compared to Mountain or Cave, so I can't say that this is like Dragon and Normal (no effect) either. Could it be possible that Steel favours BOTH Cave and Mountain?
Either way, someone else will need to do Steel too. I might have time to do another run today on my Black cart unless someone else does it first.