Michigan Booster Seat Law Booster Seat?

Booster seat? - michigan booster seat law

I live in Michigan, where the law says that "needs to 4'9" a booster seat. My question is that my uncle had a friend 7 years ago. Driving a huge truck with extended cab Dodge. Obviously, the child sits in the back seat, where it is safer. permanently provided under the height, so you need a booster seat. But the head of the window each time your father a bump! without the seat is relatively small, does not touch the window sill and to the glass. Are there exceptions to the law? I mean, if it came from an accident, it would be better to head struck the seat and not glass?