I spent 30+ years in the filter business and strongly support what EngineerMike stated. Testing clearly indicates the oiled foam elements are not nearly as efficient as paper/resin media. Taking this further, at the risk of sounding harsh, if filter element Life is more important than Efficiency to you, simply poke bigger holes in the element.
Also, do not try to save a few bucks by blowing out the element because pressurized air can damage the media. If you must, because you see higher than normal Delta P on the "Filter-minder" somewhere in the Boonies, remove the element and gently tap it on the ground to release some of the dust. Then re-install it to get you to someplace you can find a replacement (I carry a new element). Always make sure there is no dust around the sealing surfaces of the element and housing.
Generally speaking, low readings on the "Filter-minder" indicate less restriction, which is synonymous with lower efficiency. Note: "Filter minder" gages are not all that accurate and, for myriad reasons, the same filter element installed to other housings with their own "Filter minder" can indicate differently. They are best used for reference only.
As FRAM used to say; "Pay me now or pay me later".
Bob (Squidly Down Under) & Peg - 2013 Ford Focus pushing a 2011 Phoenix Cruiser 2552S
"In God we trust" to preserve our country and bring our Troops safely home.
Carry on, regardless..................