Transducer of the HC-SR04 and general trasducers angles

Hi guys ,thanks for taking the time too help.

Ok what I would like to know is the hcsro4 datasheet says that it has a Effectual Angle: <15° and a Measuring Angle: 30 degree what is the difference and what angle is the sound actually coming out at.

I found this waterproof transducer

I cant really make out what angle it is?(sorry still learning what everything means in datasheets).

It also says its Max. Detectable Range is 2meters, is this with the bounce back of the sound so if it didnt need to bounce back to a reciever would the max range be 4meter?

Another thing is if you remove a transducer from the hc sro4 board and put it say 40cm away from the board and connect it with 2 wires will it still work will there be any timing issues etc?

Thanks
M…