The time signiature is not important, the phrasing is. If you write tango with the shorter measures, then it is performed with a bit of a two-measure phrasing.
Some of the step combinations seemingly leave you with an incomplete measure or phrase, but that's because the combination shouldn't break on figure boundaries, but on musical boundaries.
Consider for example two walks and a link. S S QQ __ with an unfilled S left over. That's usually the initial slow of a closed or open promenade or something, but the thing it it's also the conclusion of this phrase, a releasing of springlike compression in both the bodies and the music.
Going further, think about how it's often common when starting (in practice) in promenade in the swing dances to take a preceding step out in PP on the last beat of the previous measure before beginning the figure. In tango we are actually doing the same thing, only the figures are in effect defined across barlines. Suprised at that idea? Look at how the ISTD actually defines the foxtrot figures - they go across barlines too, though it's more common at least in the US to change the definitions of feather and three in order to be able to teach them each as 3 measure-aligned steps.