When I was a mechanic in the Air Force they did a lot of research on plugging in vehicles, this is what I remember
after 2 hours your engine is as warm as it is going to get, being plugged in longer has very little effect. Wind may change that, but I haven’t seen that on vehicles with enclosed engines. We plug everything in on a timer
block heaters (frost plugs) are the most efficient, and you use less electricity for the same result
for extreme cold silicon pad heaters on the oil pan(s) and battery heaters offer huge increases in startinG. My diesel trucks have a 75w on the oil pan, 60w on the tranny, and a 60w battery pad under each battery. I also have added battery maintainers on newer vehicles (they have a small draw and it really drains the vehicle at 50 below). When I worked on the USAF fleet we also added them to the hydraulic system and some of the odd stuff got an element in the reservoir.
Around here lots of people leave an old comforter over the hood to try and keep some more heat in, they see, to be happy with it, I don’t know
your engine oils have a huge impact on starting, having the right oil for the weather
I personally do not like the exterior heaters like those called tank heaters, but they do have there place. The huge Katz tank heaters we had on the dozers were really something, and had to be plugged into special 30 amp plugs.
I have seen Katz block heaters at NAPA, and all the other National parts stores, and even seen them sold on Amazon