I made very thick triangles from rockwool. I filled all four corners (wall to wall) from floor to the ceiling. Triangles are of course touching the walls - no airgap at all. But today I found this on Ethan's page
"Likewise, fiberglass placed exactly at a rigid boundary does nothing because the air particles are not moving there. And since there's no velocity, the fiberglass has very little effect. As fiberglass is spaced further from the wall, the air particles passing through it have greater velocity. They are slowed down as they pass through the fiberglass, which converts the sound energy into heat therefore absorbing some of the sound."
Is it same with the rockwool? Should I move my triangle towers of rockwool away from the wall? If yes, How many centimeters ?
At the exact point of the boundary there is precisely 0.00... velocity, but... as you move ANY distance from the boundary the velocity will increase. By moving your traps away from the wall, you gain absorbing higher velocity "waves" that and you can space your very thick triangles away from the wall to optimize their efficacy. This is the point where you may want to take acoustic measurements because the dimensions and modes of your room will come into play with your bass trap positioning. As you experiment with different distances from the wall, you should find the optimum spacing.
The only caveat with spacing is that if you go too far (like more then double the thickness of the absorber) you will get "holes" or losses in the frequency range you will effectively absorb (that's usually a bad thing). As said before, testing will show you the way.
All that said, most who build super chunks like you did often place them directly in the corner. There is nothing wrong with that either...but if you have the room to move them out, experiment and take measurements if you want to know for sure!
Rock said it well. I will add that I do gap my super chunks and probably because I've measured them to perform better that way. As I recall, this was a contentious point at the time but measurements don't lie. For what it's worth, my front super chunks have an angled rigid panel behind them. Sometimes it pays to double wrap it, so to speak.
My front two chunks are spaced 24"x20" off the walls. I have a rear chunk spaced 7" and another spaced 24"x42". These are 2'-half fluffy chunks. The reasons I have one spaced 42" is due to my hall partly bisecting my room in addition to the modal issue which it causes.
So, start by stuffing them in the corner then inch them out until you find what works best.