Underwater Vision on Air Units

What exactly does the underwater vision on air units do?
For example, when you run a frigate above a sub you can see the sub as the unit it is, but when you do the same with air units you can only see the grey blobs (actually the wrong one showing a surfaced unit).
Does the unit need to be in contact with the water (surfaced oder submerged) for the water vision to toggle?
I don´t know if it should be any different balancewise, just curious...

On another note, what´s the reason for UEF and Aeon T3 scouts not having sonar? It´s been brought up here (https://forum.faforever.com/topic/5297/give-uef-and-aeon-t3-scouts-sonar?_=1682873208099) but nothing came from it.
Is there any chance to implement it or would if throw off the balance somehow?