I would think that any metal you put between the fire and your pan will drastically increase your boil times. Best you could do would be to raise your pan a little when it's ready to be pulled off and slide a piece of sheet metal in at that time. When my syrup is getting close to being done I let my fire almost burn out so I don't have much flames coming out when my pull my pans.
Dan of Jack & Daniel's syrup.
2021 - First time tapper, 40 TAPS, 7 GAL syrup, 400gpd RO
2022- 105 taps, 17 gal syrup, 2x 400 gpd RO
2023- 143 taps, 27 gal syrup New 12x16 shack. Lost my father in law Jack who helped me build it. New Badgerland filter press.
2024 - 210 taps, 37 gal syrup, 6x 400gpd RO Procon pump