BUT, registers might be on the outer walls and still not exactly under windows. I had a house like that. One notable register is located to the side of the dining room by the stair well rather than under a window. Another is in front of a closet at the end of a hall that is windowless except for the window in a door leading to the outside.
Most are and a heating contractor gave me the explanation I recounted in post #31. I guess YMMV. If there is no register under the window there will be more cold induction from the window.
I did account for 'other locations' in post #37.
Another is in front of a closet at the end of a hall that is windowless except for the window in a door leading to the outside.
Putting a register next to an exterior door is a really bad idea. Too much debris would fall into it from the traffic. I would question the competence of any contractor who did that.