Well I guess in tango turn is always completed before placement so it will always be "between" and not "on".
But, yes, I too was thinking there should be a slight body (or at least upper body) turn L between 2 and 3 (and possibly 3 and 4), with, of course, no turn of the feet (I am thinking in terms of the man's steps).
I guess at this level it comes down to the turn of the body relative to the feet in the promenade compared to the non-promenade position.
But sometimes, even though my upper body turns slightly L, I sense myself turning my hips slightly to the R at the end of this figure. And I am not sure whether this is incorect, or whether it simply means that the upper and lower parts NEED to move in opposite ways.