My filters always have a certain area that gets dirty before the rest of it. Must be where the incoming air hits first. Normal in my observation.
Oiling. There are all kinds of filter oil on the shelves and for me, that's where they stay. I use Rotella in the crankcase and the air filter. After cleaning and drying the filter I put it in a ziplock bag, add oil, knead to saturate, remove, then wrap several paper towels around it squeezing to absorb the excess.
I'm sure someone will be along shortly to extol the virtues of No-Toil products.
Gray-haired riders don’t get that way from pure luck.