Two tables home tournament question

Often at our home games we'll find ourself with more than 10 players but less than 20. Which means that we have to divide the numbers of players evenly amoung two tables. With 13 players we'll have a table of 6 and a table of 7. My question is at what point do we combine tables. I say that the final table should not have more players then the starting tables. For exp. when we have 13 tables we'll combine tables when there's 9 players left. But I think we should combine when there's 7 or 6 players left. Thoughts?