diff --git a/cumulusci/tasks/bulkdata/mapping_parser.py b/cumulusci/tasks/bulkdata/mapping_parser.py
index <HASH>..<HASH> 100644
--- a/cumulusci/tasks/bulkdata/mapping_parser.py
+++ b/cumulusci/tasks/bulkdata/mapping_parser.py
@@ -195,7 +195,10 @@ class MappingStep(CCIDictModel):
         elif values["api"] == DataApi.SMART and v is not None:
             assert 0 < v < 200, "Max 200 batch_size for Smart loads"
             logger.warning(
-                "If you set a `batch_size` you should also set an `api` to `rest` or `bulk`."
+                "If you set a `batch_size` you should also set an `api` to `rest` or `bulk`. "
+                "`batch_size` means different things for `rest` and `bulk`. "
+                "Please see the documentation for further details."
+                "https://cumulusci.readthedocs.io/en/latest/data.html#api-selection"
             )
         else:  # pragma: no cover
             # should not happen
Coverage and warning for SMART API+batch_size