Most surgeons will use templates for marking the areolar in theatre. These will usually be from about 4-5 cm. It is best to discuss this with your surgeon.
A Breast Reduction usually involves not only a reduction of the breast but also a reduction of the size of the areola to match the breast proportionately. Most, if not all reductions offer some type of areola reduction unless specified by the patient beforehand. Discuss your goals with your plastic surgeon. Like any procedure, the idea is to select the safest , most effective one that best meets your goals. Best Wishes