Mass/weight distribution?
I think the OP meant Mass(weight) distribution.
I think the standard distribution mentioned is approx 60% rear wheel, 40% front wheel.
With an aero bar set-up the weight distribution should be similar because although the bike will have a steeper seat-tube angle & the rider will be in a more 'forward' position, the distance between the bottom bracket & the steerer axis should be increased. That is one reason why putting aero bars on a road bike is a compromise.