The point being that on these experiments, the sensor isn't an array of piezos, rather a single-element piezo. Cuts the costs (a fab invoices around 100-200e for such a sensor), but lowers the overall image quality.

I wonder if two sensors placed at a distance can make a huge difference, and how/if the image quality converges as you increase sensors.

One of the next experiment is to try with 8 small elements ;)