as you can see on various pictures, there doesn't seem to be a specific bass trap in the corners of the angled sidewalls. even if that was the case, you could still place them "behind" the "rockwool-ed" side walls (you have an inner & an outer shell).
homatherm istmore reflective regarding the low frequencies, but i don't think regarding high frequencies.
If you look only at the resistance to flow aspect of things, then in theory, Homatherm indeed shouldn't be as good as Rockwool in the LF.
On the other hand, if you take in account it's mechanical behaviour (and tortuosity factor etc) and use that, then it is far more effective than Rockwool in the LF.
So it's not only about the tool this time, it's about how you use it
and how you install it. It's important to see beyond impedance tube tests and echo chamber tests. And, in time and as experience grows, learn to read that data from another angle.
Homatherm, depending on the quality of the batch (believe it or not: if it's made of newspaper or magazines) may not absorb 100% in the lower mids, but around 0.8, 0.9. - which as soon as you've place the fabric and dacron layers, isn't a problem at all.
The side walls do contain membrane systems behind various layers of various absorptive products. It is not allowed to put any pictures of these in build threads though. So you will never see them on GS or any other forum. Side walls are pretty deep.
Re: geometry.
Except for front wall, you have to see how this works depending on the frequency bandwidth your dealing with. For High frequencies and Mid Frequencies, obviously, seeing the type of treatment used, it does not make a difference whatsoever. So there you are correct!
For lower frequencies, the point is to avoid having to control residual modal behaviours from the shells as much as possible, which can be hard to fully eradicate in rectangular spaces. For that, controlling dispersion of sound, and thus redirecting it to a specific area of the room (back wall in FTB) and being able to "map it" rather precisely is needed. That brings much better results than leaving the room rectangular, if you know how your geometry will behave precisely enough.
To do that you work on the way LF see the shell and how they interact with the complex boundary of the side wall's first layer of lower impedance treatment for example ( homatherm, rockwool etc, HF + MF treatment), membranes (LF pressure based treatment) and higher impedance boundary (wall, soundproofing and geometry). When a wave hits resistance to flow treatment (the first layers of the side wall traps), there is a change of impedance hence a change in direction of the sound and a phase shift. When it hits the membrane, a massive phase shift and loss of energy/pressure. When the residual energy hits the hard shell, a phase shift again + depending on frequency either a surfacic behaviour or a geometric bounce (Snell-Descartes like).
Also, the angle at which sound hits porous material will make it "see it" differently. A controlled angle of incidence can greatly enhance the performance of certain type of treatment in the LF, basically, for any frequency where the behaviour of sound isn't yet fully surfacic. Now that is a whole can o' worm here because indeed, when LF get low enough and incidence low enough, they will tend to "follow the surface of the trap" rather than actually interact with it. So you need to deal with that too.
So basically, geometry is one of the tools in the box to control LF behaviour in the rooms and optimize it.
This is vastly generalized (and probably full of typos) but should answer your question, I hope.
