bake, roast, grill, dry by fire
烘 centers on applying dry heat to cook or remove moisture: baking, roasting, grilling, or drying something by fire.
烘 combines 火 (fire) with 共, which likely contributes the sound and may suggest a shared or communal fire for cooking or drying.
Fire 火 on the left and 共 on the right: picture a shared fire where everyone gathers to bake and roast food together.
For コウ, imagine a coal fire baking bread: coal -> コウ, and the fire 火 dries and roasts the dough.