Maybe "smaller" outside rearview mirrors, IMO, and somethng like these (and/or wide-angle overhead rearview):
Autobahn side view convex
I recently
increased the size of the mirrors on my truck. Having a larger field-of-view at a distance (behind travel trailer, rear bumper of which is nearly 60' back from driver) means better gauging of who/what is coming on behind me.
Best FE is mainly about being lane-centered under all conditions . . so the information provided by mirrors has much to do with the time & extent of driver energetic inputs to the vehicle. The fewer and the lighter,
the better.
And not just when towing.
.