The minimap has always been relatively the same throughout the series.
You only see enemies when
- they have been spotted by other players (will show both on minimap and marked in 3d)
- they fire their weapon and you are close enough to hear it (except for enemies who have silencers equipped)
- teammates who look at enemies should also spot them on the minimap if they are looking at the enemy long enough but not mark them in 3d (this might have a max distance though, not sure)
But you cannot treat the minimap as a radar like you put it.
It does not detect every single movement on the gamemap like in games such as Halo.
So yes, its possible that you get killed from behind by a knife without you ever seeing the enemy coming on your map.
Recon classes usually have a few gadgets that help with spotting enemy players for a longer and automated duration.
So, the clue to communication in battlefield is SPOT SPOT SPOT, always spot!
When should you always spot?
- Always spot when you see groups of enemies moving in a certain area that you cannot reach quickly enough yourself or that will flank your teammates.
- Snipers, always spot snipers so your own snipers can counter them.
- Enemy armor! the last thing you want is a sneaky tank flanking your teammates because they did not see it coming, always spot enemy tanks and alikes!