You can select which field Synci should base payee information on. Most banks include this in the sender/recipient fields. We recommend leaving it on "Automatic" for most people, as Synci will attempt to use multiple fields to appropriately populate the field. This setting is available under Bank Account > Settings > Fields.
You can check out the values of the available fields by clicking the "..." button on a transaction. Every field we have received from the bank will be available under the "About" tab.