OK, as I see it, the front calipers hold more fluid. That's a given.
The front calipers also require more fluid movement than the rears due to the larger piston volume.
So, with that in mind, the MC is designed to send more fluid to the front than the rear.
I assume that there are twin chambers of different sizes that the MC piston operates in. It must have two different size piston seals on the piston shaft.
Therefore, you will see more movement of the fluid to the front brakes.
There may also be a bias built-in to the MC design to delay the fluid one way or the other.
As far as fighting the air battle goes, back in the day when brakes were simple, pressure bleeding with the pedal worked well. Now days you need a pressure tank bleeder, or a vacuum bleeder. Too much tubing and other devices for air to get caught in.