As in all Circular sets for Couples, the 2-couple square set is formed by the Dancers being evenly spaced in a circle with the Ladies Standing on the right of their Partners. The Top couple is that nearest The music. The 2nd couple, at the Bottom, Faces them, Man to Opposite Lady, i.e., much as 1st and 3rd couples in a 4-couple square set but with no Side Couples and separated by only the same distance as that between Partners.
Carisbrooke Castle, is an example with no Progression, the dance being performed once through with both Couples having an equal part.
Scotch Mixer is an example with that form of Progression in which The set breaks up toward the end of each Repeat; then The sets reform for the next Repeat from any pairs of Couples who happen to be adjacent. Note that this particular dance is also Progressive by Couple in that the Dancers exchange Partners immediately before The set breaks up, too.