If you look at it in reverse - coming from the blower to the filter, the flow makes sense with the bottom of the very wide oval pipe opening up directly into the round diameter of the filter. I'm not sure why the filter is sitting behind the radiator, or for that matter in the engine bay at all but:
A: The shorter, larger path to this type blower, the better.
B: Ed is a very smart guy
C: Don't think he makes custom inlets pipes without some math behind it.
D: Maybe not the first one he made for this.