It also factors in other things. Variety of wheat. like Cyclone Dave said, keep a clean sample but try not to mutilate the straw. Many times to get the grain(white caps) out we run our concave as closed as possible. This year especially straw has been very tough. Has a shinny appearance as though its too wet to combine, but grain is dry. Even our 480 lexion with a cylinder then rotors chews it up bad. Another thing probably obvious already would be the original height and harvested hight of straw. Not to be bias, cause I love JD Balers(our 535 anyway) but I've heard New Holland balers will pick up the straw behind a TR. Read it in New Holland Powermanager several months, maybe a year ago now. I know our 535 won't pick it up, and our new 567 is worse than our 535. HOpe this all helps!