Along with the blowby, oil from the crank and cam are whipped up and carried thru the blocks vent holes in the lifter valley. This whips the hot oil up onto the bottom of the valley pan. Where it has a chance to condense and fall back into the block and down to the pan. Also helps keep the oil away from the pvc or road draft tube when installed in the rear of the intake. And also collecting and burning on the intakes exhaust crossover as you mention if not in place. From what I've read and understand the blowby might be more sensivtive to the intakes with rear pvc or road draft tubes. Than the later valve cover filter and pvc systems. As it's the oil is fairly condensed at that point when it reaches the heads. So I'm not sure if that is anymore an answer that a statement? What type of engine is your problem on? FE or other?