Hi,
Sounds like you have lowered the height of the air inlet if its now by the front grill, are you sure it will not allow lots of water / moisture to be taken up ?
Always replace my air filter once a year, even good quality ones like Blueprint are cheap enough if you shop around, as DeTomato mentions.
K&N do a standard air box filter for the Diesel and say you only need clean them at up to 50k miles intervals.
My only concern about a high flow filter of any type, is will it adversely affect the engines performance at all, seem to remember seeing some forum posts about folk having such troubles when using them...?