Both the Transmitter and the Receiver are soldered on the same PCB. But the Receiver receive the sound "directly" from the Transmitt(I don't know how).
To make it work, I have to separated them at least 15 cm.
(worked with reflection)

I've buy one module, the sonars are on the same PCB, within 1 cm of space between. How can they do the job?

Stanley