The rewards change and go down every time I complete a level
For example, the reward was 200 soul ash, and the next floor was a bit higher. I completed the 200 soul ash level, and the reward for the next level went down to 100
How does this work exactly? Should I just complete the highest one every time?
Yes. Doing the higher one nets you the reward of every previous floor.
Doesn’t it mention that somewhere in the Torghast interface when you queue? I think I heard my guildie say that but since he’s usually the one queueing us up, I’m not entirely sure.
Lol I just checked and it does 
Well next time I’ll read carefully
Oh it is there, heh.
As I said, I wasn’t sure since I’m usually not doing the queueing, but I do remember my guildie saying that.
Yes, the amount of Soul Ash per floor is largest on Layer 1.
So I did Wing A Layer 1, Wing B Layer 2, Wing A Layer 3, Wing B Layer 4, and so forth while progressing, to make every run feel more rewarding.
Once done, completing a higher Layer gives reward as if you completed all the lower Layers, so yes, only two Layer 8s (or any Layer you are comfortable with) per week now.
Correct, the numbers go down as you go higher, that way it is less punishing for players who are unable/don’t want to do the higher layers.
But yes, completing the higher ones grants the reward for all lower layer ones. So completing layer 8 grants all 570 Soul Ash (the cumulative total of rewards from layers 1-8).
So you only need to do the layer 8 versions of each one to get the full rewards.
That is why you will do your top layer each week thereafter only. You get rewarded for all levels below the one you do each week if you didn’t already grind the lower levels that week. Diminishing return in a sense.
Once you can clear it, you can just run the max layer each week and collect the full rewards for that wing.
Yes.
It gives people a large chunk of ash early so that everyone has access and then marginal increases that accumulate doubling the soul ash at max level.