Books were printed and movies are made on that subject often countering each other.
During many years I found that spreading paste gives best control of amount of paste. Too much is problem only in case it spills over the side but too little may not cover full IHS. I spread it thick enough not to see letters on IHS and leave about 2mm at edges not covered. Pressure will do the rest. Mounting cooler makes more difference than amount, it should be done in one go, not taking it off or letting slide around. If you have to lift cooler off, smooth it back again.