Expect the answer to be counted in syringes per side, and ask for that number in writing before you agree to a plan.
One published guide gives a range you can compare any quote against.
The range Hubmed gives
Hubmed's guide to cheek filler results and midface rejuvenation states that most midface treatments require one to two syringes per side. It adds that for younger patients with minimal volume loss, one syringe may offer a subtle improvement.
Notice two details. The count is per side, so a quote should say whether it covers one side or both. The one syringe example is tied to minimal volume loss, so it is not a default for everyone.
Related reading
For general background on injectables, see OHSU's page on dermal fillers. Lips are a different area, but Cleveland Clinic's guide to lip augmentation, fat transfer and fillers is a separate reference if you are weighing both.
Getting the syringe count into your plan
Ask your St. Augustine provider to state the number of syringes per side in your plan. Then ask what result each amount is meant to give you.