One thing you can do to greatly reduce the dust intake is to set up prefilters at the point of intake as like in this video. I can set you up with what is needed if you like by contacting me at email@example.com
This will greatly increase filter life and when using multiple pre filters it allows you to work down through the stack to maintain clean filters for a longer period.
Last Edit: Sept 24, 2018 14:10:54 GMT -5 by The Fool
I haven't had the opportunity to work with the 4s air box, but I have heard it is a bit of a pain. I can find out what the K&N replacement is if I had dimensions of the stock filter. Hopefully some other 4 owners will chime in.