In the past, I used to block the grill (not all but most of it or the lower area and leave the engine air intake area free) on several of my cars with use of the block heater to keep the heat a bit more. I remember my '88 CRX where the engine temp wouldn't go up at all or even go down when driving with the heat setting at max and fan speed in 3rd gear plus using the engine BH. Blocking the grill sure helped on those days.
But that was when I was living in colder more remote areas with no traffic.
I don't do it anymore with a heated garage and usual Montreal gridlock.
In Chibougamau Qc and James Bay area, people would just roll the engine block heater extension cord around the passenger side mirror to use at work. I did that for a while but the copper wire inside the insulator broke at the plug from being bent at an odd angle and I had to fix it at -30C...
I would also always use a plastic cap over my exterior BH plug to prevent roadsalt shorting it.