It's a matter of a personal preference isn't it ? If i put it near the large door, it could help offset the cold air coming it but if the door gonna be open alot then it would be wasting energy. If i had it in the back corner of garage but i don't work in that corner, it's gonna feel drafty don't you think ? This being said , we need to know how you plan on using the garage and what are you storing in there and where do you park your tractor.
12x11 overhead door in front left corner. work bench in front right corner. new holland 1920 , 6 ft. finish mower , brush hog , back blade , rock rake, and allis chalmers d 15 scattered throughout.