Weirdly enough I do was my entire neck and shoulder area after a head wash (top to bottom basically), because if you think about it, the water washes the dirt from up to down, so you need to clean the dirt down into the drain (quite literally).
Gravity tends to cover the entire body with shampoo anyway with a light scrub. It has always confused me though why we need soap and shampoo if shampoo cleans the head it should be able to clean the rest unless it makes your genitalia burn then I'd recommend finding different shampoo all together
I get severe dry head tried so many medicated shampoos just tried head and shoulder apple cider vinegar and it seems to help a lot more, oh plus your head can smell like apples and no one would question your manhood.