Well in real life over/under is based on the offenses strength of formation and which lineman you want your 3tech(Best Interior Rusher) going against to either stop a rusher and or get an ideal matchup. 3-4/4-3 isn't really important since the difference between a 3-4/4-3 front is strictly based on personnel, the postions on the field are roughly the same. Nickel 2-4-5 is just taking away a NT in a 3-4 for a DB instead of the SLB in a 4-3. And double A gap IRL is to confuse blocking assignments or merely overload the center to get quick and hard to avoid pressure. 3-3-5 wide in a run defense with Nickel personnel, its essentially a 5-1-5 defense that stacks the line. Dime is to defend better against the spread more DBs vs more WRs. Most of this doesn't apply to Madden so someone else would be better at that but for real life thats kind of the gist of it