What is the correct orientation for the engine air filter on a 1999 ML430?

The filter pleats are "stepped" with a long and short section. The pleats obviously install facing down. But is the filter installed with the longer pleat section closest to the front of the vehicle or closest to the firewall? It fits and seals either way but must have been designed this way for a purpose.

Thank you very much,

Jim

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Jim Herold--Current: 1987 190E 16V, 1999 ML 430--Past: 1971 280 SL, 1972 250