I had the same problem. I replaced my AN backplate with the SE one. So far, no oil spray - even in heavy rain. (I have a Dewey Rammer open air cleaner cover.)
I have BIG-SUCK AIR no problem.... and just wondered right after cleaning YOUR air filter HOW LONG from that time until you notice the problem........ HOURS or MILES please....does it leak- by during first ride??? This will let us know a little more... also WHAT brand and weight engine oil do you use?....