Applying the lessons from bats...

What would have determined the 90 degree disposition of the parabolas signals and the 180 degrees one respect to the other,  instead of straight at the ends of the 'ears tube'  ?

Some systems used four horns, with one pair giving the direction and the other pair the elevation. This configuration might be a way of getting both components.  

edit:

That device carries a note that “When tested at the Dutch military research station at Waalsdorp it was found it “contained fundamental deficiencies”.”

https://rarehistoricalphotos.com/aircraft-detection-radar-1917-1940/