We usually try to match them within a few inches (usually no more than 1 hand) but what is more important than the height is the stride and how well they work together. In the last pic with the draft horses, we were worried that they wouldn't match up because the black usually has such a long stride and the mare has a shorter stride. However, after hitching them up, the black takes shorter strides in harness than he does loose and they match up very well. Quite often, they will be on the same stride. A team that matches perfectly with size isn't worth much if their strides are totally different.