That Club SOP sounds like its not saying the same thing as the flight manual.
In the light piston singles I fly, I have fuel flow gauges, so I lean in the climb to the figures the flight manual says to lean to.
Otherwise, lean gently in the climb, taking note of the sound of the engine. Err on the side of slightly rich - but leaving the thing at full rich is poor technique. Even below 5000 feet, engines still work better at a correct fuel-air mixture.