I want to use the ultrasonic sensor under a metal grid plate like below (just 1 of those plates instead of 3). The sender/receiver will be under (partly inside) two adjecent holes (hopefully it fits) and point upwards. The reason is to detect if someone (a person) steps on the plate.
The height of the plate is about 1,5 cm and the height of the receiver/transmitter is about 0,5 cm (if I leave some space for the enclosure), maybe even less space.
What I'm worried about is that the receiver picks up the distance to the plate (the red lines), so it will always received just a centimeter or so.