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

Short side to the front.

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90 300TE 4-M
Turbo 103, T3/T04E 50 trim
T04B cover .60 AR
Stage 3 turbine .63 AR
A2W I/C, 40 LB/HR
MS2E, 60-2 Direct Coil Control
3" Exh, AEM W/B O2
Underdrive Alt. and P/S Pulleys,
Vented Rear Discs, .034 Booster.
3.07 diffs 1st Gear Start

90 300CE 104.980
Milled & ported head, 10.3:1 compression
197° intake cam w/20° advancer
Tuned CIS ECU
4° ignition advance
PCS TCM2000, built 722.6
600W networked suction fan
Sportline sway bars
V8 rear subframe, Quaife ATB 3.06 diff

Do you know the reason why the short side goes to the front? As I look at the inside of the air box, the bottom of the box slopes but is basically flat. I can't figure out why the filter is designed this way.

Thanks again.

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