Visibility in WW2 rules

I have tried to come up with a simple yet realistic way to handle visibility in my WW2 rules in development. As players we can of course see the entire table but in battle it is often difficult even work out where the shots being fired at you are coming from.
The system
Two types of target; infantry and infantry support weapons, everything else.
Basic visibility distance; 1000m for infantry/infantry support weapons, 3000m otherwise.
Now this is modified by a series of situations that halve the spotting distance and these situations are cumulative:
Target neither moved or fired last turn
Target in or behind cover (a wood, hedge or building for example)
Target entrenched
Conditions of poor visibility like; heavy rain, snow, mist or night
Observer is a tank within 1000m of enemy – this is the situation when a tank crew ‘button up’, when they come under fire
So as examples; a tank driving across a field in the open could be seen at 3000m, the same tank behind a hedge and whilst snow is falling could be seen at 750m
Once a target has been spotted then it can be ‘seen’ by all the units in the opposing army and continues to be spotted, unless or until line of sight to it is physically blocked (something like a hill or building in the way would do the trick). Of course you cannot actually see through blocking terrain (see hill/building).
Now Recon units role is to detect the enemy, when they are performing a spotting action, they double the visibility distance, so for example could see a tank moving, at 6000m!
Seems a simple system that gives a bonus for being the defender and entrenched.