It a convention that doesn't apply to many. For example, this convention has no more veracity than KOPS. Neither apply to me...I like the handlebar in front of the hub and I have ridden with every combination.
You can perform a simple experiment. Test the handlebar covering hub convention both on hoods and in the drops...it changes.
What that means is your bar height matters and your visual viewing point depends on your torso angle...and look how differently people ride in terms of handlebar height...no convention there...you just recently going for a riser stem. For me, the higher the handlebar the farther the bar needs to be forward to preserve reach. A guy will longer arms like me will need the handlebar more out in front than a guy with short arms.