example: 20 frigates are chased by 30 dolphins; only frigates at the end line will shoot while those on the front will be blocked cause frigates can't shoot over each other; in such case frigates that have enemy units in range but cant shoot could have indicator, small sign eg some red round icon in the corner of the unit which will tell the player he can micro better these units and do not utilize them to the fullest; such icon could appear eg only after 2 seconds (best if parameterizable) of "not shooting" so that it does not blink the icon on/off all the time; I think often players do not understand which units shoot over each other and which doesn't so this would help them micro better; in given example dolphins group would not have such icon because they can always shoot over each other as I understand
#Widget idea: indicator of unit not shooting because allied units stand in a way
stuck matrix
terse mantle
example: 20 frigates are chased by 30 dolphins; only frigates at the end line wi...
this is a really good idea, though I wouldn't know how to do it.
dusty summit
I guess you would copy whatever shows 
when you're E stalling?
half steeple
Would need a little engine modification, to be more specific about what is blocking firing.
Spring.GetUnitWeaponHaveFreeLineOfFire
Probably works, but cannot tell you if ground or features is blocking your aim. (and is probably not great for performance)
north briar
Good idea! Is the type of blockage(terrain/features/units) really relevant?
dusty summit
Probably not! In either of the cases, your reaction is the same (move the unit).
thorn sparrow
stronk idea