If geocoding this activity, the location would definitely be Turkey. Thus the recipient-country should also be Turkey. “Syrian refugees” would appear in the activity title, description, perhaps results etc, which would help find it if needed.
If this is reported by country B, it presumably becomes in-country refugee costs (note that this cannot be reported for all migrants, only refugees). The question seems rather about the nature of the funding/spending than the location.
(As a side note: these are questions that should be addressed by the DAC, not IATI. I don’t know that we have a mechanism to relay, or at least highlight, to the DAC the need for guidance in the community beyond CRS reporters.)