"AFAIK the standard tactical sub-unit of mounted knights was a "squad" of usually five men"

Well some claim that knights were organised in such a way but that's pretty dubious. In actuality their tactical organisation was probably exactly the same as their logistical organisation, i.e. that they fought with other knights from the same manor, military household, mercenary company or whatever. That might have been five knights or it might have been some other number depending on the particular case.