Your math is good for the area. (pi r^2 = l x w). Mine is straight up, 90 deg, too. The quicker you get the heat close to the underside of the pan, the better. As long as you leave enough room for the length of your wood, 20 inches should be fine.
2017 - 20ish taps on buckets, boiling outside in two baking pans
2018 - 70+ taps, 14-buckets, 50+ on tubing, homemade arch from oil tank in my barn, 17 gal syrup
2019 - same set up, 20 gal syrup
2020 - less taps, short season, but RO kit was fantastic! 6 gal syrup and a maple cat!
2021/22/23 - expanded into the neighbors yards! 50 taps on buckets and 40 taps on tubing