The Shopify Billing Address details are mapped to the MailingStreet/MailingCity/MailingState/PMailingostalCode/MailingCountry fields on the Payment Txn.
The Shopify Shipping Address details are mapped to the OtherStreet/OtherCityOther/State/OtherPostalCode/OtherCountry fields on the Payment Txn.
If any of the Mailing Address details are different to the Other Address Details then the Billing Equals Shipping Address is set to False, otherwise if all match then it is set to true.