Not exactly yhe answer your looking for but i connectwed a 6 inch fan with reducer to a 4 inch carbon filter my room temps were too high so i took off the filer and reducerr and it easily keeps temps down now.How much do duct reducers effect airflow? Specifically a 6 inch 400cfm inline fan with a 6"-4" reducer? Asking because tent hole is smaller than my fan and hood.