If your mini screen is focus on the bottom of the map cause he's being shot at by a rocket luncher then you wouldn't be able to see the enemy coming from the top cause it's focusing on the tank being attacked.
The mini screen is their so you can see the whole map and be able to rush your tanks to a spot as quick as possible.
What you have is a good idea but I would do it different other then focusing on one tank or one building.
Since 99% of enhancements aren't made.
Taking your idea and just making it simpler

have the mini map show the tanks and buildings being attack in a green or a color that isn't cyan, blue, red, yellow.
I think it would be better if the map creators could make it happen on some maps instead of all the maps just to spice every map up alittle different.