International Style Tango
The commencing stance for the Tango uses a parallel Third Foot Position; the resultant "torque" will place the man's right hand further across the lady's spine.
Because of this position, forward walks with the left foot will be taken in CBMP, while forward walks with the right will be taken with the right side leading; conversely, back walks on the left foot will be taken with the left side leading, and back steps on the right foot will be in CBMP.
As a consequence, the walks will curve to the left.
There is no rise and fall in the Tango. The footwork on all forward walks should be H and on back walks should be BH.