here is the anti-drainback valve.
The pump has to force the oil under pressure through the holes, which forces its way past the soft seal. Depending on the material, thickness, etc, the amount of force may be significantly different from one brand to the next.
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That's my theory anyway. I could be wrong.
That different filters result in different oil pressure values has been observed many times both here and elsewhere, so that part of it isn't really in question.
Lol, that went over some folks head!