In the second example, must be terminal/approach airspace to have 3 mile sep, I suppose.
Heavy can descend as soon as they have passed under Canadian rules (reciprocal tracks, diverging by more than 135 degrees, when you have tail to tail you don't need any further separation).
Light can climb when it is 6nm from the heavy's PRESENT position, which will probably be A+2 given the speed difference.
You don't need A+6 (separating by 6nm from where it was 2 minutes ago? why would you do that?) because that would be the same as giving about 15 miles of wake separation if it was passing behind the 767 as opposed to underneath. The wake 6nm behind the 767's PRESENT position will be exactly the same regardless of the direction of flight of the C402.