I think so...
This is not correct,you could have as little as 10mph difference and you will still see the symbols. It will just take a little longer before they register.
If you are gaining on the enemy you will see the- symbol,just remember the distance icons are not exactly accurate,at D200 the enemy could be as far as 299 yards or as close as 99 yards,this is why we have the symbols so a player knows if he's gaining or not.