In the case of “Bridge” there were less obvious tonal components to the field recorded sounds. I mean the reverb of course has some frequencies that stand out, but it’s not as obvious as in “Cavaedium”, where the plain recording of the space already sounds like a synth drone in some cases. But I guess that by layering all those sounds there is a lot of spectral content going on, with overtones from one sound sounding like they are the overtones of another, and there might be some auditory illusions deriving from it. I have this thing when I try to guess a pitch of a sound by ear, that sometimes I mistake the first order overtones for the fundamental.
So I guess that I have to admit that I do not really know, and I definitely didn’t do anything deliberately on the track, but still, I’m really happy that it does that for you! 