I think there is no one right answer for all situations; but for punkfolkrocker's specific application the creaking of bellows does seem undesirable. Simply placing the mics in line with the ends should help to emphasise the desired sounds from the reeds over the undesired sounds from the bellows. For greater suppression, might it be worth deliberately recording the bellows sound with another mic on a separate track and then doing some subtraction in the sound editing?