Create a loop, then test it
A lengthwise return and intake near the downstream zone often form a useful loop, unless wood and rock divide it.
A low intake can receive solids but must avoid substrate and livestock. Surface film requires upward momentum or overflow capture.
Use observation as a tracer
Watch harmless food dust and record settlement. Change one height, angle or side at a time.
Do not make fish fight a narrow jet to compensate for poor distribution.