Cheers! I look forward to hearing how you go.
Another thing I tried was reversing the transducers into a 5cm parabolic dish, to increase gain and directionality. Since the wavelength is around 7mm, this should yield gain of 5x in the forward direction. In the direction-sensing system, the better directivity should make it easier to process multiple echoes. Never pursued this far enough to get scientifically valid results...