I’ve found there are large umbris chunks as low as 120-125, also. 300 in about 30 minutes this time around.
As you can tell by the other posts, Umbris has a real good range. If You’re not having luck, go up/down by 10 degrees and you’ll probably find a sweet spot or two.
IMO the range has it’s greatest variance in worlds with prefabs like we have on this planet currently. It really forces the player to move around a bit because there are large holes at the end of some of these rock clusters. At least in the area that I was going crazy in.
This is a great bit of trivia. The last Umbris world we had I had a lot in glacier. Ended up having a few stacks oof that darker red glacier as a result.