How much control do doctors have over the resulting breast size?

I am sorry you did not get the result you hoped for. Predicting breast size after breast reduction can be difficult. Cup size is not an accurate method for achieving predictable results because cup sizes are not standardized from one bra manufacture to the next. In general, the more tissue I remove, the more opportunity there is for me to damage important blood supply and sensation because the blood vessels and nerves are housed within the breast tissue itslef. That means conservative breast reductions that make modest changes in volume tend to be safer than dramatic breast reductions that remove large amounts of tissue. There are exceptions to this rule of thumb. The blood supply to your breasts is as unique to you as your fingerprints. So it may be that your surgeon encountered a blood supply issue he/she did not expect.

It would help to see photos. However your surgeon is correct. The pattern for breast reduction is pretty standard so you can’t necessarily choose your final breast size. It’s simply the nature of breast reduction surgery

During a breast reduction consultation it's important to discuss your goals for surgery so that you and your surgeon can develop a realistic plan. The risks and benefits of the procedure should be discussed prior to surgery. However once surgery begins your surgeon must adapt to the situation at hand in order to give you the best result which includes adequate blood supply to the tissues. More information would be needed to comment on your specific situation. The best person to answer your questions is your surgeon as she/he is most familiar with the details of your case.

The final size of the breasts after breast reduction depends on many factors and one is the blood supply issue.

In doing a breast reduction, we must keep enough tissue to keep the nipple alive, or resort to doing a free nipple graft. In some areas, tissue must be removed because there may not be enough blood flow to support this area and your surgeon wanted to avoid fat necrosis with hard balls of scar tissue. Once healed, if you are not happy with your smaller breasts, then add implants. You may find you love the size.