With your feet too far back you are not parallel.
Sorry we have drifted away from collapsing the maul question but.......
With a long position you are closer to parallel than with your feet underneath you. Also if more upright you are setting up at right angles to your bigger muscle group so cannot push forward as effectively if at all, and will have a tendency to squat and lift driving up and through the opponent (illegal) or hinge and go down, (also illegal), especially when you oppo drives over on top of you, much more difficult when you have a long straight back to transfer the force.
Tower of Power, although very fashionable, seems contrary to any manual handling advice. If you were pushing the scrum machine or a rucking sled, or even a car for that instance, you would not set up a tower of power, your shoulders would be low and you feet would be back! Pointing upwards sufficiently to unweight the device a little but putting most of the effort parallel to the ground.
Additionally, when the front row set up square the hooker doesn't seem to have optional channels; 1, 2 and 3 into which they can hook and give a variety of attacking options, although with the number of squint throw ins nowadays hooking is not the skill it once was.
Perhaps the Tower of Power is the cause of and not the solution to scrums being a shambles.