I’ve played many good BKCII games on a 4’x4′ board, with most units on 50mm x 25mm bases. I simply reduce the number of units fielded, or vary their arrival so that it doesn’t get too crowded, plus come up with a scenario to suit the smaller table.
For a table of around 3’x3′, In Her Majesty’s Name, KR-16, The ‘Songs of’ series and Dux Bellorum all work very well, as they are designed for this size. I’ve just invested in ‘No End In Sight’ which again is designed for the smaller table. It seems popular at present to go down this route as many of us have limited space. However most of these games can be easily scaled up should space allow. Hope this helps?