I rarely say something like that, when i don't know from experience. I train medieval fencing a lot, and we have tried that way of fighting. It does not work. The shield has to be on your shoulder, so that you can be bashed with another shield and still keep the formation. And it is hard to do this and keep the spear overhead. Probably they used both ways as Asgaroth said, but we can not use it in rtw. (or maybe we can... i have to see something ).
Whatever - basically we keep it vanilla, and i'm working like that.