Trying to merge multiple mono and poly Wave files while piping (to add custom padding to each input file.)

Whatever I do, on input poly files the output channel order is totally unpredictable.

I’m using something like sox -M “| sox 3ch.wav -p pad 1” “|sox 5ch.wav” -b 24 output.wav

I would expect to get the same order of output as in the order of the input / pipe, but that does not happen.

Now, remix could fix it, but I need to know what logic behind the channel remapping is used, and I am clueless…

Thanks for any insight!