I don't see how adjusting the gap would affect slippage much. The gap mainly just determines if the magnet can initally pull-in the clutch, but once touching it is mainly the electromagnet force * friction that keeps it from slipping. There would be slighly less spring force fighting it if you reduce the gap, but probably fairly negligible. The oil on your clutch plates is probably the culprit in the slipping, plus adds to the smoke as it fumes off.

I am glad you posted this. My 1985 car's AC clutch started smoking years ago. I assumed the compressor had seized, but later found I could turn it easily. You now make me suspect it was an "oil on clutch" issue. I have a Sanden on there now, but kept that R4 and still use an R4 on my 1984.

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1984 & 1985 CA 300D's
1964 & 65 Mopar's - Valiant, Dart, Newport
1996 & 2002 Chrysler minivans