I think the default convergence is about 330 meters.
As for setting it to 70, that might be physically impossible.
To have the wing mounted guns converge, the armorers are essentially turning them around inside the wing. In that sense, the amount of available "wiggle room" within the wings places a limit on your convergence choices: to set point blank convergence the guns might have to be angled so much towards the centerline of the aircraft that they can't fit in their rectangular bays anymore
