In order to reach proportional representation, the Belgian Constitutional Court ordered a redistricting so that every electoral district has at least 4 seats. Three districts with 2 or 3 seats were deemed too small to have genuine proportionality. (The case affected the Walloon regional parliament)
Are there similar court-imposed magnitude constrains in other countries using proportional representation?
http://www.const-court.be/public/f/2015/2015-169f.pdf