I've just started running a small weekly pairs tournament with our club members, and I find that no matter how many boards or rounds we play, I can't ensure that every pair gets to play against all the other pairs. For example, in a 10 round tournament with 6 pairs, it will often happen that two pairs will end up having played against each other for 3 or 4 rounds, and having not played at all against other pairs. Is this caused by the small size of my tournament, or am I missing something?